Don't forget Cleveland, which always tries to get into the mix for point guards. They'll probably offer Wally's contract plus draft picks in a sign and trade, although they don't have a lot of other assets.
I wouldn't include Cleveland. Why would GSW want to do a sign-and-trade with Cleveland? They have nothing to offer to expiring contracts.
Cap space right now or pay bad players money for a year and cap space then. For Cleveland to be an option in this they'd need to be able to put some quality young players on the table along with the expiring contracts and then the other team might consider it.
For the the same reason I don't think the Cavs have a shot at Elton Brand.
There's nothing to gain by doing a sign-and-trade. GSW and the Clipps should and will turn down any offers for a sign and trade with Cleveland.