Wildstarsreach, I don´t think you are getting the rationale behing capping for spellcasters and not capping for psionics.
Spellcasting capping makes sense because no matter how high level the spellcaster becomes, the resources invested in casting the spell remains static. A Magic Missile spell is always prepared in a 1st level slot, no matter if the wizard is level 1 or 20. If he´s level 1, he spends a 1st level slot and deals 1d4+1. If he´s level 20 and without capping, casts magic missile, he´d do 10d4+10. Resources spent remain constant, but benefit provided augments freely: the spell becomes better with time.
With psionic powers, on the other hand, if you spend 1 pp in, say, energy ray, you always get 1d6 damage (or 1d6+1, or 1d6-1). It doesn´t matter if you are level 1 or 20, you spend 1 pp and get 1 die. While the cost quickly becomes trivial, you always get the same effect, no matter what. If you want to improve the effect, you have to pump PP in it; say you spend 10 extra power points to deal 11d6.
Now is when you say "That´s broken! a 1st level power shouldn´t do so much damage!" But the power remains a 1st level power on paper. You´re not spending 1 pp any more, you´re spending 11. With 11 pp you´d be manifesting otherwise a 6th level power: instead of energy ray, he´d be using Disintegrate, or an augmented Energy Current or whatever, with probably greater effect and the same cost.
With spells that doesn´t happen. A 10 dice magic missile will be vastly inferior to a 9th level spell, but the resources invested on it will continue to be a meager 1st level slot. A 1st level slot may become too good if allowed to freely scale too much; that´s why there are caps on them. Maybe 10 dice are too much, but how about 5 dice?
Now suppose you cap psionic powers. At 11th level, instead of being manifesting Energy Ray and Disintegrate, the psion is manifesting only Disintegrate (because energy ray capped long ago and is no longer useful). You´ve not made the psion less potent: you made him a one trick pony, stuck with low level powers he´ll never use. You didn´t solve the supposed problem with psions (that they can manifest many high level powers) and alienated why many like about psionics (that they are flexible). Summarizing: you made psionics worse.