Storm Raven said:
No, since the rogue/mage has a lower caster level than the straight wizard, meaning that the base power of the rogue/mage's spells is generally going to be significantly less.
The reason you should stop DMing is that you didn't figure this out on your own.
Once again, I urge you to ease up a bit. Harsh comments like these are simply not needed or appropriate.
The rogue/mage can, under very specific and limited circumstances, do more damage with a touch (or ranged touch) attack spell.
Of course, how much will depend upon how many rogue levels he's got. More rogue sneak attack damage = less mage power, which in turn means fewer and lower level spells.
Also, this is restricted to only when the bad guy has no Dex bonus or (for touch attacks in melee only) is flanked.
Relax. This won't unbalance your game. It may
seem really powerful, but if you compare it to a pure wizard or pure rogue, you'll see that the single-class character pretty much wins out every time.
Your player has created a sort of one-trick pony. No big deal, really. He won't always be able to use his little trick, and he'll run out of spells soon enough anyway, especially if they have to face more than one encounter in a day.
Sure - he can use a wand for this. So can a pure rogue with Use Magic Device - it's DC 20 - not too easy, not too hard, really. He sidesteps that by taking a level of wizard. Okay, a fair trade-off. And, unless he takes a fair number of Wizard levels (at least 5), he won't be making his own wands.
Relax - use the rules as written if you can. Only vary from them if:
1. You really, really hate the rule as written.
2. The rule is a bit vague as to how it works.
Do that, and your players will thank you.