I think you are going to have a hard time getting an exchange of equal quality for your Starwood weeks. I tried San Francisco Exchange Co. for awhile, but they didn't come through for me. Depending on where you bought, you may be better off renting and then using the money to rent exactly what you want. That's what we do now.
Also, you need to see who the resort is affiliated with. Even if you bought resale, if the resort is affiliated with II, I don't think you will be able to deposit with RCI, and vice versa. Even on a resale, to exchange through II, you have to go through Starwood. Of course, with an independent, you just reserve the week as if you were going to use it yourself and then deposit it directly with the independent exchange co., and then they contact Starwood and handle the exchange.