It's not a massive leap of logic to conclude that what Sony is now doing with Monster Hunter Portable 3 Remaster for the PS3, and other games, it can also do for the NGP. Rather than just put the old PSP versions on the NGP's PSN store, it can sell at a premium these upgraded versions and help publishers whose PSP games sold okay, but not stunningly drag some more life out of their titles.
Not only will this help fill out the release schedules and nudge gamers into upgrading, if you ignore the odious spectre of us paying for those games again, its an attractive proposition. While all the obvious candidates like Metal Gear, God of War and Final Fantasy will be at the top of most owner's lists, it would help bring back to NGP developers who had a shot at PSP and didn't get the greatest of rewards from it.
A final thought on this, could folk playing on a PSP play against those using the NGP version, allowing people to keep using their PSP's and keep their old games for friends and family to help enjoy some multiplayer fun and save the old console from the dust pile.