When all is said and done, there is a lot to be said for the inherent capabilities found in the compact/basic E-2 platform that was designed 50-years ago and incrementally improved over time. The biggest advantage is that it as designed from the ground-up solely as an aew platform to hoist a large antenna to 25K-30K ft, a fair distance from the battle group (and stay there for a while) while minimizing the impact of the airframe on the performance of the radar. It is modestly economical from a fuel consumption standpoint (better now with the new props - ditto for vibrations), though admittedly not as much as what a turbofan could provide (including a better dash capabilty) and offers true-360 degree covereage, meaning one needn't compromise one's barrier set-up to account for antenna issues (like lack of coverage ove the nose/tail).
If the E-2D works out as it seems it might, especially the new radar, it will be yet another significant leap in capabilities for ship-board AEW (and shore for that matter) that can not be matched by modifying another platform - V-22 included.
But then again, I'm slightly prejudiced
