Nail said:
[EDIT]In fact, the more I think about it, the more that seems to be the primary problem: Integration. In order to integrate, you're gonna have to boost Sor/Wiz/Clr/Drds in some way to compensate. And, you'll have to add a significant mix of psionic monsters, traps, and limitations.
Is changing the entire system worth including psionics?
Druids are the most powerful spellcasters in the game. Really, hands down. Druids don't need boosting in the face of a psion. Wildshape, speak with animals, charm animals, animal trance. A 1st level druid can possibly charm a Deinonychus (I know, because it has been done before in one of my games). Yeah, I'm getting started.
Compare that to a Telepath. A telepath can charm a person into believing that he is trustworthy and good, but not an animal. A telepath cannot connect with animals, the powers aren't there for it. OH, psionic dominate could be used, if your 10th level (Animal, fey, giant, magical beast, or monstrous humanoid). But that's at the cost of 9 power points.
The Balancing factor is in the environments both work with. Druids and rangers are great for Wilderness encounters. If you are having a wilderness campaign, Druids and rangers are completely in their element. Wildshape, animal companions, etc.
Psions and psychic warriors are great for urban campaigns. City streets, murder mysteries, detective work. The fine smell of a gas lamp. Psions shine in a campaign where they can interact with NPCs. You can change a druid or ranger to interact with the urban environment (if you go for "punk" style gaming, that is); but they are limited in that environment. They need animals to converse with.
Wizards are better than psions hands down because they have a greater versatility than the psion. The psion has a measly 36 powers at 20th level, although much psionic potential. Wizards would have possibly have more than one hundred spells written in their spell books.
A Wizard's spell selection changes daily, but a psion can only use the powers that he knows. So, if you have a dungeoneering campaign, it's better to say to your players that psions would be at a disadvantage to the campaign. If you have a wilderness campaign, psions would also be disadvantaged. In an urban campaign, they excell.