Nyarlathotep said:It's true that over the course of four or five encounters they are balanced with other spellcasters, but the problem I ran into was that after two encounters with all PP spent already the group would just retreat and rest. Sometimes it was one encounter, sometimes it was three encounters, but as soon as the PP ran out, it was resting time.
Yeah, but you are the DM, and you decide if the PCs can rest or not. A PC waking up at 8 AM and spending all his PPs until noon will not be tired, and will not want to lay down for the rest of the day if, say, he has to be out of the dungeon in 48 hours. Maybe you shouldn't allow your players to deal with their resources so lightly. As said, wandering monster do exist.
Nyarlathotep said:I'd argue the Crystal Shard is pretty close. No spell resistance or save, you do have to make a ranged touch attack, but damage-wise it's nasty (and one of our Psion's preferred powers).
Crystal Shard is a metacreativity power that deals piercing damage and is thus subject to damage reduction. And here some numbers, 'cause I like it so much

Split Psionic Ray Empowered Maximized Crystal Shard manifested by a level 20 psion would deal 218 points of slashing damage to a target, no save, no SR, but subject to damage reduction, at the cost of 20 PP.
Arcane Thesis Split Ray Empower Disintegrate manifested by a level 20 wizard deals an average 420 points of damage (Fort partial) and uses up and 8th level slot (equivalent to 15 PP).
Quite balanced, I'd say.