Yes, I am a rules whore
I have an incantrix/archmage wizard, and yes, they are broken. The reason they are broken though is because of the fox's cunning thing. This has been nerfed by 3.5 so that empowering fox's cunning doesn't work (it no longer has a variable effect). So this particular problem is solved.
I have heard the rumor that you can't stack metamagic in 3.5, but I have not heard any actual sources for this rumor, so no official word as yet. I would not be suprised, but I think this is a(nother) stupid and unneccesary nerf if it is true
On the other hand, being able to stack empowers on spells like fireball and summon monster is not really that inherantly broken. Yes, a 7th level fireball cast by an incantrix has an average of 105 points of damage, but at that level, there are ALOT of things that can take the hit.
The bigger issue with this PrC is the fact that you can easily make unbeatable DC's. However, since this has been nerfed, I don't really see any major problems with it.