Let's separate Frost from Farabee. Frost is a good target, Farabee is not.
With regards to Cates, I'd just say that Cates has more upside, that's the attraction to him. The only reason anyone talks about him is because his name came up in rumors at the last deadline. Not happening so much anymore, so maybe it's best to let go of any hopes on getting Cates.
With regards to Frost, it's speculated that Philly wants to trade him because his agent ALWAYS recommends that his players to to UFA. I don't want to give up a lot of assets to for a player who insisting on going to UFA.