Origins of magic and such
My next-to-last D&D game was set in a world ruled by a 4000 year old lawful evil monk-wizard who did, in fact, make divine magic illegal save when approved by the state, and made all religions state religions. (This lead to a magical-priestly underground, of course, but that's a different story.) So I have great sympathy with the notion that it would be possible to turn magicians into a resource.
On the other hand, trying to tame wizards has potential drawbacks -- like a powerful and disgruntled wizard can do a LOT of damage. So it could definitely backfire to treat magicians like second-class citizens. But people, at different times, can do massively stupid things, hehe.
As another aside, and something someone on this list is apparently doing by limiting one of the nations in his game to fifth level and lower spells, the notion of a "magical tech level" could be interesting to explore. While it doesn't make too much sense for divine spellcasters -- tho' it could be argued even in that case, if one had sufficient zeal for it -- the idea that spell levels 1 through 9 instantly appearing in magicians' heads is pretty dodgy, to me. It could be that each spell level -- the ability to cast spells at that capacity -- had to be rigorously invented by legions of magicians. So, for instance, a society that didn't invest in magic might have spell levels up to, say, 3, while one that heavily invested in magic might have spells up to 9. A developed, robust culture of magic might "invent" spell levels past 9.
As another aside, if magicians are the same people who would become scientists or proto-scientists, what would the presence of magic mean for technological development? Almost all of your best "scientists" would be off learning magic! This could cripple technological development.
On yet another hand, I was thinking about some of the possibilities of spells and . . . what would be the use of, say, <i>wish</i> or (clearly my favorite set of spells) <i>planar binding</i> or <i>contact other plane</i> when it comes to technology? Consider. A magician raises a devil of knowledge who tells the wizard about this easy-to-make compound, and an easy-to-make weapon that rivals the most powerful destructive magics and can be used by illiterate peasants. Yes, of course, it's gunpowder and the devil teaches the magician how to make cannons and guns with it. This could become routine. Actually go through the effort of inventing? No, no. Technological progress, driven by magicians, might be negotiating with outsiders for inventions and the like -- and it has the potential to be much swifter than <i>research</i>. After all, what fiend wouldn't want to give the humans nuclear, biological and chemical weapons?
*more random thoughts*