I've never really liked the idea of 'psionics' in any setting, wether fantasy or science fiction.
I've always felt that 'psionics' are just magic dressed up in a very very thin veneer of psuedo-science. If the setting is fantasy, the presence of 'psionics' feels redundant to me. If the settng is science fiction, the presence of psionics feels unnatural and hypocritical to me.
If a player wanted to play a 'psionicist', I'd point them at the Sorcerer class and say, "This is a pretty generic tool. Pick some spells that are appropriate to how you envision your character." I could probably even be convinced to come up with some feat trees and/or spells that would make their character concept more interesting or viable.
All that being said, I fully agree with you that the 2nd and 3rd edition psionics books left alot to be desired from a flavor standpoint. There are things that its generally accepted that psionics can do, and there are things its generally accepted that it cannot - although, this line is pretty blurry, as witness Stephen King's 'Fire Starter'. (Again, this is the reason why I think the Sorcerer is a far better fit than anything we could come up with, as it let's the player rather than the DM be the judge of what is appropriate to the character.) Still, I agree that despite the blurriness of the line, bolts of acidic energy are definately on the wrong side of it.
I suspect that you are going to be unhappy with my suggestion that Sorcerers make better psionicists than any other class (including psions), even though it addresses the question 'How do I make the two systems on the same level?' in what I consider to be far and away the most elegant fashion, so until you come to that realization yourself, I'm happy to help you with any design problem you are having.
My first suggestion would be pick up a copy of the 1st edition PH (still the best resource flavorwise) and copy of the 2nd edition Complete Psionics Handbook. Collect together the powers that you think have the right feel, and discard those powers that you don't think have the right feel. Adapt them to the 3.5 edition Psion, and drop any 3.5 edition powers you feel don't have the right flavor. I don't think you'll need to do much beefing up of the 3.5 Psion, as the general concensus is that it is at minimum as powerful as a cleric or wizard, and probably slightly more powerful.
Personally, I think that psionic points are problimatic. The 1st edition psionist escapes the problem by not being a class and not being meant to compete on the same level as magic. He doesn't learn, expand, or develop his repetoire and so he doesn't need to worry about balancing defensive, offensive, and utility powers. He has what he has. The powers he possesses are merely random boons, and sometimes a curse (when facing a more powerful psionic creature, he may be dead before the rest of the party can react), so the fact that they aren't balanced isn't even an issue. The problem with points is that it encourages 'Alpha Strikes' where you dump all your points into the repeated application of your most powerful abilities. This turns into the infamous '15 minute adventuring day' faster than even the most spellbound wizard.
Psionic combat existed in 1st edition DMG and was almost certainly the inspiration for Troy Dennings telepathic combat (since he started out as a D&D writer). There was a quite detailed system, although I never had recourse to use the rules, as in 15 years of DMing, I never once had a psionic 1st edition player character. My appraisal of the rules though they are quite evocative, they wouldn't be much fun in actual play. Psionic combat occurred as an in round subsystem which used a much faster time scale. The result would be that two psionicists would enter combat at the beginning of the round, engage in several rounds of draining each others points off - and quite possibly the weaker of the two would die or go insane, before anyone else in the party would get a chance to move.
Thanks for the reply.
The Sorcerer solution is certainly balanced. However I am running Dark Sun, which means that most everybody is going to have limited psychic power, and I would rather not nitpick spell choices for not being "psionic" enough. Psionicists would boil down to a Sorcerer with fewer choices... while the end result would be balanced... seems messy.
I was rather surprised to learn that pyrokinesis was a complete invention of Stephen King's. Go him.
Anyway, thanks for pointing me to the 1st edition heads up. Could you clarify what the PH is? Psionics Handbook or Player's Handbook? That was a bit before my time. I had the 2nd edition Complete Psionicist's Handbook, which was very cool but very strange. I think it was that strangeness that helped make it feel different from magic.
Maybe this will help define a little bit what I want...
I wrote a sci-fi story where I divided psychics into the following types:
Pyrokinetics: The most destructive psychics, but probably the least versatile. Not good for much other than burning things.
Biokinetics: Seems a tad out of place, but this would cover applications of mind over body, that is, accomplishing amazing bodily feats thanks to intense concentration. Their control of other people's biology is limited, and even then requires touch.
Telekinetics: Nearly as destructive as Pyrokinetics, but also quite versatile. Shields, throwing things, lifting heavy objects, and levitation.
Telepaths: Use the mind to connect and control the mind. In Dark Sun, every psionicist should have enough grasp of telepathy to defend themselves in psychic combat, but Telepaths would excel at it. Also for communication and mind reading.
ESPers: Having perceptions beyond normal ability. Being able to see far away places and sense things that others can't. Abilities of precognition and postcognition would fit into this category as well. I could see talented espers going so far as having psychoportation applications as well.
I also had Electrokinetics, which don't quite fit into dark sun, and Mediums, which shared some powers with Espers, where Mediums took the spiritual side (it was questionable whether they could do anything at all, until you saw for yourself) while Espers were more rooted in real phenomenon, and the distinction is somewhat blurrier in a game like D&D.
Anyway, my ideal system would involve these types, but beggars can't be choosers.