Smith isn't terrible at PF, but you're not winning anything with him there, your best bet is middle of the road if he's your starting PF. Also, Monroe/Drummond are around the same age and would hit their primes right around the same time, whereas Smith will be toward the tail end of his career when Drummond is ready.
I would exhaust every avenue in trying to trade Smith, while keeping my frontcourt together. There's only 1 other team in the league with as talented a young (under 25) frontcourt as the Pistons, and you can make the case the Pistons bigs are better (Jazz).
Henson/ Sanders should be nice, too.