Let me clear up some mistakes on this thread:
If Pena were to get 500 AB's, at this pace he'd strike out 160 times. Alarming yes, but he'd be about 35 short of tying the record.
Though a small sample, Pena is actually playing an above-average CF. He is at a +1 in the FRAA catagory (Fielding Runs Above Average)
Pena has shown some marked improvement at the plate, as pointed out by Harold Reynolds. Reynolds states, that being traded to the Red Sox was probably the best thing that will ever happen to him. Already, Pena is showing that he can go the other way. The knock on Pena before was that he was too eager to pull everything. That hasn't been the case this year. Though he will blunder often, he's still a work in progress. He has however, showed that he can work on the things he needs to develop in order to be an elite hitter.
Lastly, I do agree that being moved to AAA would help, but it's a moot point.