hong,
Very interesting idea! The explanation that caster potency reflects your inner "strength of spirit" or some such is certainly plausible enough for me. However...
First, a smaller objection. I don't think melee/spellcasters are too weak. I've played with fighter/wizards, barbarian/clerics, and the like who were evenly split... and they were quite effective in melee combat. Not quite as effective as a straight fighter... but with properly chosen spells and feats, they were reasonably close, plus they had all sorts of nifty non-combat magical abilities. The melee/spellcaster combo seems balanced enough to me. A spellcaster/spellcaster combo, on the other hand, does strike me as pretty poor. I've never seen a cleric/wizard in my campaign, and probably for good reason. (Then again, who knows... the people I play with have a habit of surprising me with creative ways of making their character effective.)
Second: there are too many low-level spells that scale up very well at high levels. You mention one example: Magic Missile. Invest one level in sorcerer, get 5 missiles. That's 17 points of damage that's very hard to avoid... which I think is pretty decent even at the higher levels (particularly when haste is ubiquitous, and you would just fire off five missiles as your partial action).
So that makes me a bit wary. But, okay, five Magic Missiles isn't terribly unbalancing. So let's pick a better example. Divine Favor. I think any fighter would have to be crazy not to take one level of cleric and get +6 luck bonus to hit and damage with a first level spell. Stack that with Shield of Faith: +5 deflection AC for 20 minutes. Or consider the 17Rog/3Drd, melee touching with flameblade (1D8+10+sneak) and protected with fully powered-up barkskin (+5 natural armor for 3 hours, 20 minutes).
Now, of course 20th-level characters can and should be very powerful. I just think that because of how many D&D spells scale, the tradeoff is just too good. With this system in place, a 19Ftr/1Clr would be (I think) a lot better at melee than a 20Ftr -- and have nifty noncombat spells to boot. There's too much return for too small an investment.
Very interesting idea! The explanation that caster potency reflects your inner "strength of spirit" or some such is certainly plausible enough for me. However...
First, a smaller objection. I don't think melee/spellcasters are too weak. I've played with fighter/wizards, barbarian/clerics, and the like who were evenly split... and they were quite effective in melee combat. Not quite as effective as a straight fighter... but with properly chosen spells and feats, they were reasonably close, plus they had all sorts of nifty non-combat magical abilities. The melee/spellcaster combo seems balanced enough to me. A spellcaster/spellcaster combo, on the other hand, does strike me as pretty poor. I've never seen a cleric/wizard in my campaign, and probably for good reason. (Then again, who knows... the people I play with have a habit of surprising me with creative ways of making their character effective.)
Second: there are too many low-level spells that scale up very well at high levels. You mention one example: Magic Missile. Invest one level in sorcerer, get 5 missiles. That's 17 points of damage that's very hard to avoid... which I think is pretty decent even at the higher levels (particularly when haste is ubiquitous, and you would just fire off five missiles as your partial action).
So that makes me a bit wary. But, okay, five Magic Missiles isn't terribly unbalancing. So let's pick a better example. Divine Favor. I think any fighter would have to be crazy not to take one level of cleric and get +6 luck bonus to hit and damage with a first level spell. Stack that with Shield of Faith: +5 deflection AC for 20 minutes. Or consider the 17Rog/3Drd, melee touching with flameblade (1D8+10+sneak) and protected with fully powered-up barkskin (+5 natural armor for 3 hours, 20 minutes).
Now, of course 20th-level characters can and should be very powerful. I just think that because of how many D&D spells scale, the tradeoff is just too good. With this system in place, a 19Ftr/1Clr would be (I think) a lot better at melee than a 20Ftr -- and have nifty noncombat spells to boot. There's too much return for too small an investment.