Honestly, I'd be surprised if you could get Santana and something else of value for Cabrera. In my experience, those holding the top 3 SPs in the league are very hard pressed to trade them for anything, much less as part of a package 2-for-1.
Since Santana's pitched excellently and has a good record, his owner's probably going to be more hesitant to move him. Instead, I would probably try to fish for Hamels, Haren, or Peavy and a mid-tier closer (ideally, the team who holds one of those three needs a 3B and has an extra closer they could part with) like Cordero, Soria, or Valverde. I would think that would be a more logical deal.
I encourage making an offer to the owner of Santana and Wilson, but I wouldn't expect them to take it.
I wouldn't take the first trade at all, and don't expect anyone to give you Santana for Cabrera much less Santana and a closer. However with Pujols and Longoria you could move Cabrera to help your team. IMO with your team I'd hold on to him. That's 3 big bats, 4 with Soriano.