bit of necromancy, but having read the entire thread I figured why not comment all the same.
.
I would alter the saves part, Instead go with something like
At level 21, You gain proficiency in two saves of your choice, if you are already proficient in all saves then you instead gain a feat instead of proficiency in a save.
.
Or if like many games you allow resilience to be taken more then once, simplify this to, you gain two feats.
.
As for proficiency, I would likely suggest allowing it to continue to scale, As is at level 21 the save DC and Save bonuses are already to a point where bounded accuracy more or less breaks down anyhow. Easy to just add more monsters in that give bless like effects, and of course epic monsters and such.
.
also tactics for monsters can make quick work of things still, stuff like maze often takes a player out of the fight, brutal if that players the healer, and beholder with invulnerability and a good tactical location can be devastating to even epic players if you mix a few monsters in.
.
I think for the most part your quick and dirty rules would work just fine.
.
Epic level games are not for inexperienced DM's, and unlike most of %e it should be just fine to take it outside the normal bounds a little.
.
That said things like Extra attack not stacking does hurt many melee classes, and others like druid who already hit there capstone do not really benefit from taking druid further.
.
Ever concider just making a Epic version of the classes, a more or less bare-bones design to address issues where certain classes really don't work the best taking them for a second 20 levels?
.
It is just there's a great disparity in 40 levels of Rouge and say 40 levels of Druid, in what is gained from those levels.
