I would say a 6th is a bad trade, a 5th is acceptable, and a 4th is good.
Look at the whole picture, Moulds will be 33 year old before season starts, he doesn't want to wear Bills uniform anymore, and he doesn't want to take a pay cut. Everyone knows Bills will either release Moulds or be forced to keep him with a high cap hit as well as have negative impact from him next season.
What draft picks did Eagles get from Owens? None.
Moulds' and Owens' situations are not exactly the same, but are somewhat similiar. Both teams have cap room, both players don't want to play for their teams, they both were dued to a roster bonus, and there're other teams showing interests in them while they're still with the teams.
Moulds is not a cancer in the locker room like Owens, but it doesn't justify why Bills can trade Moulds for draft pick(s) and Eagles didn't.
Marv did a good job handling the whole Moulds situation, 4th round or not.