Marcus Smart is almost impossible to put a value on for me.
On one hand, you look at his stats and he sucks. That's not exaggeration; he sucks. Can't put the ball in the basket, doesn't do anything else well enough to make up for it.
On the other hand, you watch him play and he can change games when he's on the court. He's capable of taking over for short stretches, and if there's a loose ball in crunch time then he either caused it or got it. Very good defender who can play bigger than his size.
Like I said, I don't know how to evaluate that. Is he ideally a sort of mini-Draymond? A fourth starter who would fail as a go-to offensive option, but thrives playing alongside elite scorers where he can focus on doing everything else. Or is he just a defensive-minded bench guard? Obviously the equation changes if he develops an adequate skill on offense, but right now, I wouldn't know what to pay him.