Well, it just mostly seemed to me that, after 20th level, characters don't advance very much at any given level. A 21st level wizard has, like, 2 more spells than a 20th level one. Every 2 levels, a wizard would have a major jump in power as he gained a new spell level, but that kinda dies down at epic levels. Mind you, I never looked closely at epic spells, so maybe I missed that one.
yup, you missed the improved spellcasting feat which grant you one spell slot of one level higher than your current max level.
The wizard get one bonus every three level through her class, and one every three through her character advancement, that's 2 feats every three level.
It means that if a wizard improve her spell slot every two level, she still has one feat every four level that she can spare on something else, and given the stength of some epic feat (improved metamagic), I'm pretty persuaded that the wizard keeps her steady advancement in power.
The increase in number of spell is taken care of through int boosting item.
The only real decrease in wizard advancement is the low Will save.
However, you did make one error. Hero is a class just like fighter. All classes get, for free, the same BAB and save progression beyond 20th level. Like I said, I didn't really look too closely at the book, so I don't know whether epic feats should be closer to 4 HrPs or 8. However, if all a fighter is getting at those levels is the (free) BAB and saves, plus 1 feat, a few skill points, and 6 more hit points (11 as opposed to 5), that's not too much.
The problem here is that FCTF is supposed to work without ELH, and I asssumed that the n/a on save and bab past level 20 meant that it didn't advanced.
So, finally if you change nothing, the cost would be 8 HrP for two level and it would seem balanced.
The problem is that some Epic feat are really powerfull, if a wizard can take improved metamagic, epic spellcasting, Epic intelligence, and Epic Spell Penetration with just two hero level, no wizards will ever continue in his normal class.
If you price epic feat at 4 HrPs, you'll probably need to raise the number of HrPs per level up to 6.
That's why I think you should put the price at 8 for Epic feat, and let the number of HrPs increase by 8 every level for ease of use (if you create your NPC with HrPs and wants to determine its level after, it's easier to just divide by 8).
Eh, like I said, I didn't pay too close to the ELH, so these are all kinda rough assumptions. It probably doesn't play out in reality. One thing I do know, though, is that at high levels, a large chunk of PC power comes from magic items, which to me is a brilliant shame.
It's the legacy of the "door/monster/treasure" standard adventure. It doesn't bother me that much. By the way, could the formula that you used to determine the number of HrPs obtained through gp deficit be extended for Epic level?