Perhaps we should see what's the max cha we can get with the best eq nowadays, and base it on that? I would guess it's around 4-5 cha for each slot, but I might be wrong.
However, I'm not sure how casters and non casters stand.
The way I see it, cha is capped. So if you got perhaps +5 cha equipment for each slot, you could hit 100 cha easily, and max out your casting potential.
But DR isn't capped (technically it is, capped at the very best eq).
If the situation as it stands now, casters are much better (read: overpowered) than melee classes (in terms of overall ability), by all means, raise the max cha vastly and have that maxed amount have the same effect as 100 cha.
But if melee classes are much better (read: overpowered) than caster classes, increase cha to 150 or 200, but leave damage formulaes unchanged.
But if they are roughly the same, then raise the max cha to the highest available cha possible via equipment, then have that maxed amount have the same effect as 100 cha.
For the above three situations, I'm assuming that the classes are decked out in their best eq, maxing their CHA / DR (and relevant stats) respectively.
The altar idea sounds fun though. Much better than the race bonus at the start.