This is precisely what I do; DC = 10 + 1/2 CL + ability mod + misc
You realize that this doesn't increase the DC of their highest level spells, right? (It actually lowers it in some cases). It increases the DC of their lower level spells, but that just gives them a bit more versatility and a few more rounds of usefulness in a day. In practice, it doesn't boost their raw power much.Yes, the one thing high level spellcasters absolutely need in 3rd edition is a boost to the power of their spells.
Isn't that kind of dumb, though? Doesn't it make more sense to have fewer spells, but that also scale with level?IME, at high levels, players only use their character's higher level spell slots, and the lower-level slots are "baggage".

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.