I would go with the 8 you listed. I'm not too fond on keeping Burnett, but I'm not sure if I would be willing to take the risk on one of the younger players either. Gordon, Aviles, Butler, and Masterson all have a lot of potential, but here are the reasons why I hesitate to keep them
Butler - Inconsistent; will need a year or two before I see him reaching potential/hype Gordon- Will need a year or two before I see him reaching potential/hype Aviles- You already have Tulo Masterson- Not sure on what role he will take next year (SP or RP)
I like Gordon better. Pence will go a couple of rounds earlier in ADP so he should be the one kept, and I'd then trade for some draft picks and grab Gordon. However, sometimes this is not possible with lower level keepers and I'd rather be forced to inherit Gordon than Pence. Most of their stats are similar although Pence has more 2008 HR (25 to 16) and 2008 RBI (83 to 59). Their OPS, SB, runs, avg are all about the same.
On the other hand, Pence declined in OPS from .899 to .784, avg from .322 to .269 and OBP from .360 to .318. Also, his K's and BB's stayed unexciting. Gordon, meanwhile, had his avg go from .247 to .260, his OBP rise from .313 to .350 and his OPS jump from .724 to .782. He also increased his walk rate from 6.8% to 11.6%. With his age and behind-the-scenes stat increases, I could see a nice power spike.
So, to me, their stats are similar but Pence needs to rebound, while Gordon is trending up. Add in that Gordon plays 3B, is a year younger, has better pedigree, and that I'd rather draft a young guy trending up over a guy I'm hoping to rebound............and I still like Gordon better!