To begin with, I personally wouldn't pay him more than 5 mil. But even if the market thinks he's worth more than 6, I don't think he's worth more than 6 to the Kings. We already have Rudy Gay and DeMarcus Cousins. Not many teams have as dominant an interior force as Cousins - Thomas could bring more value to their teams than he does to ours (by the way, we've seen his value for 3 seasons now; his playing style isn't going to change).
Personally, I believe this Cousins/Gay talk as the be-all-end-all nonsense. So SA has Duncan and Leonard. I guess they don't need Parker? Tell that to SA. You need multiple playmakers on your team, just like SA. Gay is certainly no playmaker; Cousins could be if he put his mind to it. Stauskas might be. McCallum maybe. That's a whole lot of maybies. Unless they totally luck out with whomever their sign and trade partner happens to be, they come out of it worse off.