It depends on what you're selling... Some watches, like a SOSF will always command a good price, because they're hard to come by, but others, probably will not sell for much.
If they're ones you don't wear much, there's not much point in holding on to them, but I would advise against selling for the sake of selling, as I suspect the new watch would fail to live up to the expectation, and you'd wind up with buyers remorse. Sure, you could then flip said gen for what you paid for it, but you probably wouldn't be able to replace everything you'd sold which you might start missing...