Currently, Mental Toughness itself gives 105 SP. Improved Mental Toughness gives another 105 SP, making that a total of 210 SP.
This can be quite expensive on some builds, and most people don't even bother taking it (Sorcerers - because they are feat starved, and Wizards - because they can usually find + DCs more useful than the SP, unless they are arch mage, then they need it as a prereq.)
I have played a WF Archmage, a WF Sorcerer (which is my current main toon), a human Cleric and Favored Soul, capped all of these toons, so I speak from some experience (chime in if I'm incorrect). I've taken them through a decent amount of endgame content to have a clue of what I'm talking about. I have not played a bard or an artificer, so anyone with experience in those viewpoints should help me out here, and give me their thoughts on the viability of this.
Anyway, back on topic, how useful can this be endgame? Well...let's look at this through a couple of different view points.
Clerics
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These guys don't have any SLA's or any cheap heals (besides the radiant servant burst, but that's free and doesn't require SP). If they took both Mental Toughness and Improved Mental Toughness, they would get 210 SP. Assuming no metamagic feats are in use:
Cure Light Wounds, Mass - 25 SP
Cure Moderate Wounds, Mass - 35 SP
Cure Serious Wounds, Mass - 40 SP
Cure Critical Wounds, Mass - 45 SP
Heal, Mass - 50 SP
Do some math here, would equal about
8 cure light wounds, mass
6 cure moderate wounds, mass
5 cure serious wounds, mass
4 cure critical wounds, mass
4 heal, mass
Of course, they can also use the spell points to do other things, but from an endgame point of view, most 'healbots' do not do much but heal and DP. They probably may implosion or blade barrier trash mobs, but that's a mute point until someone proves me wrong else-wise. More than 50% of the time in raids (i.e. ToD, Shroud, other raids), clerics and favored souls spend their time healing.
These two feats offer those heals without metamagics meaning it could easily be interrupted by trash mobs, boss aggro, or taking damage else-wise. They are also probably not very strong (assuming the average pug without very much heal amp to make it effective.
I guess they could also use the SP to buff, but meh.
Favored Soul
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These guys are currently in the same boat as clerics, look above for the math.
Sorcerers
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Sorcerers get very nice SLA's by picking their Savant PrE, and since metamagics are free for those SLA's, mental toughness could prove useful.
I won't bother doing the math here, but 210 SP could do 105 niac's cold rays for a Water Savant and other similar SLA's, and that can be very dandy. However, this requires two feat slots, which is a lot, considering the other feats a sorcerer needs to take. Most sorcerers choose to leave it out of their builds because they have other feats they need to take.
Assuming a human sorcerer (8 feats), the minimal feats they would need to be efficient endgame are
Maximize, Empower, Toughness, Quicken (to survive epic mobs and raid bosses, otherwise can be substituted by very high concentration score), Spell Focus Evocation (prereq for savant II) and Heighten. That's 6/8 feats. Most sorcerers will also take a spell focus feat or PL: Wizard if they have it. That's 7/8 now, which is what every non-human race gets.
*it's a bit late for me, excuse me if what I say is completely illogical*
Wizards
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Wizards! Unless they are archmage, I don't think many of them take the feat anyway. They are less feat-starved than Sorcerers, but they just don't have the use for it. They don't have SLA's (unless archmage) and so for a Pale Master (which most fleshies are), most spells cost a lot more. From a CC/Necro point of view:
Web - 15 SP (+ Heighten and Quicken increases cost)
Sphere of Dancing - ~45 ish SP (DDO Wiki doesn't have SP cost so I don't know exactly) (+ Heighten and Quicken)
Wail of the Banshee - 50 SP (+ Quicken)
Hold Monster, Mass - 50 SP (+ Quicken)
This 210 SP will provide about 4 of these spells for the wizards. 4 spells. For 2 feats. That is a bit...costly?
Sure, they get 5 more feats than sorcerers, but again, those could be used to increase DCs rather than to use on 4 spells.
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I don't have experience with Bards or Artificers, so I won't say anything about that, as that may make me seem stupid or unknowledgeable.
Anyway, what I want to suggest (after showing my logic/math/whatever) is to increase the viability of such feats.
The idea would be to add a line of enhancements with Mental Toughness. (separate from the current line of enhancements that do not require mental toughness; i.e. Favored Soul energy of the scion). This would be similar to the line of enhancements added by the Toughness Feat.
So, using Favored Soul as an example again:
Option 1~ (Original Idea)
Favored Soul Mental Toughness I
Requires Level 1, Mental Toughness, Costs 1 AP
Increases the total benefit you receive from Mental Toughness by 45.
Favored Soul Mental Toughness II
Requires Level 4, Favored Soul Mental Toughness I, Costs 2 AP
Increases the total benefit you receive from Mental Toughness by 50.
Favored Soul Mental Toughness III
Requires Level 7, Favored Soul Mental Toughness II, Improved Mental Toughness, Costs 3 AP
Increases the total benefit you receive from Mental Toughness by 55.
Favored Soul Mental Toughness IV
Requires Level 10, Favored Soul Mental Toughness III, Costs 4 AP
Increases the total benefit you receive from Mental Toughness by 60.
Change the benefit values however you like, but the general idea is presented there. Every caster class would have a line of enhancements. This would increase total SP by another 210 after taking both mental toughness feats, thus doubling the effectiveness of it but costing APs.
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Option 2~ (Added due to Feedback of Teharahma)
Change the Mental Toughness Feats rather than add a line of enhancements.
Change Mental Toughness so that instead of 10SP at first level, and 5SP every level after, perhaps change it so that it is a percentage value instead.Make it percentage based;
Mental Toughness; increases your SP pool by 10%
Improved Mental Toughness; increases your SP pool by another 10%, for a 20% total.
i.e. Mental toughness should grant 10% extra SP.
Improved Mental toughness should grant another 10% extra SP, thus making it 20% total increase.
This should increase what one can do with their SP, and increases based on what one has as their current max SP.
Person with 1000 SP
----w/ Mental Toughness : +100 SP
----w/ Both Mental Toughness : +200 SP
Person with 2000 SP
----w/ Mental Toughness : +200 SP
----w/ Both Mental Toughness : +400 SP
Person with 3000 SP
----w/ Mental Toughness : +300 SP
----w/ Both Mental Toughness : +600 SP
This would make taking the feats viable (as most other feats can usually do better than 105 SP), and actually make people consider taking the feats.
For the person with 1000 SP, this would be WORSE than the current feat situation. (ever so slightly)
For the person with exactly 1050 SP, this would be the same as the current feat situation.
For the person with over 1050 SP, this would be BETTER than the current feat situation.
I assume most people with 1000 SP (bards, artificers, maybe paladins and rangers with enough gear?) would not invest in the Mental Toughness line unless they really want it. With the exception of spell singer bards, most warchanters/virtuosos put feats into other things. Artificers could invest a feat or two into this line, but they could really be using it elsewhere (same with Paladins). Arcane archers would need mental toughness (or a different feat) in order to take that PrE.
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Option 3~ (EnjoytheJourney and Aesop's suggestion)
Increase viability of Echoes of Power?
maybe have Mental Toughness improve the top end of EoP to 20SP and per tic to 6SP. Improved MT could go all the way up to 30SP and 10per tic.Someone explaining their ideas better than I explain it.One way to make them more attractive is to make one of the benefits of selecting them not only more SPs, but also an increase in the maximum total of Echoes of Power, and an increase in the speed with which Echoes of Power helps casters regain SPs. It's a thematic kind of bonus to add for those feats, as well as (potentially) helpful enough to at least consider taking it.