@Chris Gunter, well said. I think you've captured my own thoughts on psionics.
To me psionics shouldn't be another class of spells--but a different kind of abilities all together.
I think that the roots of magic (fantasy) and psionics (sci-fi) make a lot of fantasy gamers who aren't keen at mixing the two, uncomfortable. Unfortunately, it's propelled a constant overhauling of psionics. I think Wizards came close in 3E, but it could still be improved upon.
Personally, I can get on board with wizards having psychic abilities while learning magic--but dedicating a "school of wizardry" to it is trying to make a square peg fit a round hole. You wouldn't teach chemistry and psychology in the same building at a university, so why not give psionics it's own cornerstone?
To me, psionics represents the side-door to Science Fantasy. Some people don't want to go that route, but it's a legitimate genre that goes way back to pulp origins of both genres. But then that's exactly why it's supplement material--it's all optional!
Great thread!