Assorted thoughts as I was listening
I enjoy sneaking, but tend to use it more for getting an advantage at the start of combat than to bypass fights completely, though it depends on the dungeon. It's great for lining up an IPS special attack, or placing traps (regular doesn't break stealth, but the mechanic time bomb will bring you out of stealth once placed), or for sneaking close enough to a beholder to fire off a petrifying runestone.
Of rogues, rangers & monks, I think rangers are the best at pure stealth, since they get hide in plain sight as a class feature plus camo & pass without trace spells which stack with items. Monks get the advantages of shadow fade for invisibility & abundant step, which lets you quickly dart away around a corner to lose enemies if they get a hint of your presence so they're probably best at the stealthy recon & evasion role overall. Rogues I think are actually the worst of those 3 at pure sneakiness, but they get those huge bonuses to attacking from stealth.
Don't overlook bards - they can be built to be as effective as rogues at the pure sneaking (hide & move silently are class skills for them too, though they don't get the ability to move faster while sneaking) & using fascinate doesn't break stealth so they can be really good for helping an entire party bypass groups by taking the lead - just make sure party members have any aura-type effects switched off first so they don't wake them up again by accident!
The red eye thing means they know exactly where you are, but you're still invisible so will still benefit from miss chances since they can't actually see you and if you can run away fast enough round a corner then go silent (ie sneak) and get further away, it's still possible to lose enemies & avoid the fight.
Underrated effects I'd say shattermantle (or improved version) since unless you're combining fighting and casting, it's more likely to require a party member giving up some dps potential to help your spellcasters do the work, but can be really useful against certain enemies with high spell resistance.
I have a feeling open lock DCs will never go above 99 - reason being, the bell of opening counts as a knock spell with caster level 99 (knock itself is caster level plus ability modifier, for an item that'd presumably be 0, so just the caster level would apply) & it'd be a legitimate reason for a refund if it didn't work, as the whole selling point of that item is to be able to open literally any lock that is capable of being picked.