It seems to me that there was a gap between them setting the additional pp cost to use metamagic (twice the equivalent spell level boost of the same metamagic on spells) and the time when they decided (wrongly IMO) to eliminate scaling of psion powers.
Maximise is an ideal case - for a wizard to maximise his 3rd level zap spell he must be at least 11th level, and it will do 60 points damage (because fireball scaled up to 10d6). For the psion to maximise his 3rd level zap spell will take +6pps onto the normal cost of 5pps, for a total cost of 11pp. Because of the pp usage limit, he has to be 12th level to produce this maximised whitefire for... ta-dah! 20 points damage. Real killer. Or he could use a 6th level power and do 11d6 to one target or 11d4 to multiple targets.
IF they had halved the pp increase for metapsionic feats to reflect the non-scaling nature of the powers they were applied to, they might be a little more worthwhile.
Cheers