I had similar "encounters per day" issues with the psion in my game. My solution:
Psions have an "active pool" equal to 1/4 their PP total. Only points from the active pool can be used to manifest powers. Transferring points into the active pool can be done by a "meditation" action; this is a full-round action (that invokes attacks of opportunity) which places an amount of PP equal to the caster's level into the active pool.
This reduces the number of PP available to the psion for an individual combat without actually taking away any PP. I found that it worked fairly well, although there were still plenty of issues with psions (the "refocus as a move action" feat, astral constructs, and Death Urge come to mind, there were many others).
Psions have an "active pool" equal to 1/4 their PP total. Only points from the active pool can be used to manifest powers. Transferring points into the active pool can be done by a "meditation" action; this is a full-round action (that invokes attacks of opportunity) which places an amount of PP equal to the caster's level into the active pool.
This reduces the number of PP available to the psion for an individual combat without actually taking away any PP. I found that it worked fairly well, although there were still plenty of issues with psions (the "refocus as a move action" feat, astral constructs, and Death Urge come to mind, there were many others).