Well, you still have to pay for each augment crystal separately, plus the cost of the additional +1 for this enhancement.
Other than that, I guess I'd have to look at some of the crystals to see what combinations you could come up with. I suppose you could get crystals in one weapon to harm several different creature types, so you don't have to switch weapons, but that's more for conviencience than raw power.
Also, you could throw three Energy Assault crystals in one weapon, but I still don't think that's super crazy. You're looking at paying an extra 6,000 gp for the two other crystals and a minimum of 6,000 more to increase from a +1 to a +2 weapon for this new weapon enhancement. It seems fine to me.