Well I think you're forgetting about Anderson in my scenario, but of course he isn't a star. But then again, neither is Gay. He's a decent 2nd scorer but he doesn't provide much else right now.
You're really not going to be able to trade Gay for a star anyway unless you attach a lot more value with him. He still has a negative reputation around the league, he's in his 30s, and is expiring. So I say again, you're not getting a star for him if he's the centerpiece in any of our trades.
It just so happens that Evans has been better than Gay in RAPM, RPM, & On/Off over the past 2 years, so in a sense, we would be upgrading in talent.
EDIT: but yes, you don't really have that true #2 star on that roster, but that's the way it is. We don't have the assets to acquire that type of player unless we want to give up the farm (Cauley-Stein, Papagiannis, etc.) which I don't want to do.
The Kings should be focused on accruing as much young talent as possible right now (while also keeping an eye on putting together a team that can compete now to entice Boogie to stay) and developing that talent to the best of their abilities. Then in a year or two maybe you have the assets to either trade for that second star or attract one in FA.