You should already be dropping Extend. It's not worth it.
(edited what I had here didn't make sense - ) Yeah extend for the death aura. )
Whether or not it's worth it on a wizard depends upon how many past lives you have stacked.
Currently I have 2 sorc past lives and this is my 1st wizard life : currently @ lvl 20 + 3 Epic lvls and the magister epic destiny intelligence maxed out I have a 46 Intelligence, that was starting with an 18 intelligence, I have had a +3 tome as well.
If you don't have lots of Spell Penetration from past lives, you absolutely must take Spell Penetration Feats on a wizard.
To be honest I never have taken Spell Pen feats, as neither sorc or wiz (i have a couple other 1st life wiz's), and have not yet to date had any issues with landing the spells (FoD, Wail) and other necro based spells, I do take spell focus necromancy (required for PM), and greater necromancy focus, so I guess that helps with the DC's. I have notice other wizards in Epics have a higher success rate than me with FoD / instakill type spells, so that could be it.
If your Spell Penetration is 31/32 before Epic Destinies and without Spell Penetration Feats, you don't need the Feats in content up through Epic Hard. If your Spell Penetration is a miserable sub-30 something, you really need to pick up these feats or do something else about it. Post your Spell Pen calculation/breakdown.
as you may tell from the rest of this, I'm not that fantastic with the mathematical side of all this (ironically) mostly to do with effort and state of mind during gameplay hours . But with everything I have including buffs I have a 48 DC on FoD (3rd Life (sorc,sorc,wiz(WF PM))): lvl23-ED(magister)
Toughness has never been a must-have on a WF wizard. Epic Elite content probably makes it a must have now. I have also appreciated it while learning the Epic Hard content, but it's not necessary there either. It's sometimes helpful, however. I'd be running around with 550+ HP if I dropped Toughness. That's perfectly adequate for all Epic Hard content, if not ideal.
I can't argue with this really, I do like to have toughness, but as advice it's solid from what I know. I just find that when I'm in a bad spot, surrounded by mobs and getting beat on, the conOps don't keep up and that last few HP on the bar can be the difference between getting that necrotic burst out that will get you back in the game, which is why I always take it without even really thinking about the addup. With buffs +items (everything) I have 618hp.