Ah, Carlos Gomez, we will miss you. I cannot crack any jokes about him, though; I do not like seeing anyone get hit like he did.
Cain washed out in 2009, but has held his own this year in the minors. He is pretty simple to figure out. His eye is developing at the plate. He pounds the ball into the ground. He can fly. He can play defense. At the very least, he will platoon in center field and start against left-handers. I think he will just eventually take over the job, and I am not buying the weak MLE because of his speed.
I think you need to bid competitively on Cain; it is rare that a starter on offense comes into your fantasy league after the MLB trade deadline. If you need steals, this is someone you definitely want to spend money on...if you need power on the other hand, you might want to look elsewhere.
Good luck with your bids!
(I am no longer putting FAAB bids on these supplemental players, as, at this time of year, most everyone either has salary cap issues or is short on available FAAB. If you ask me for one, putting the bids in brief context in your league, I'll be happy to give you my thoughts.)