Should he chose to augment the power, for each power point he expends he gains a +2 to his dispel check. Assuming the psion manifests the power fully augmented, he will expend 10 power points for a total of 1d20+20.
This is the equivelant of the psion manifesting a 5th level spell (with an extra power point left out in the dark). This does, effectively grant the psion a greater dispel magic at a lower level than, for example, a wizard, but then the two classes are not similar (the wizard gains automatic scaling in damage spells, whereas the psion must pay for it). Considering that a base psion of 11th level has about 110 power points (excluding adjustments for attribute bonuses), that quite the spend for a single power.
All in all, it is very well balanced, and not in need of a house rule at all. If the psion wants to drop a fully augmented dispel psionics each and every round, he'll chew through his power points rapidly. But that is his perogative. Remember, however, that, like most rules in the 3rd edition, the power levels are based on four encounters of roughly EL <party level> per day.