The recharge rate is too slow, and adds nothing to psions, honesty. A psion at 20th level recharges a power point every 7.5 minutes if he took two feats (and psions are incredibly feat dependant), which means that he takes over a day to recharge, compared to any other classes 2 hours (Ring of Sustenance).

Even further, gradually regaining power points does nothing for combat, since it's far too slow to ever play a part in combat, and it would require tedious amounts of time calculation to see if you get one power point during the battle or not.