I actually think this is a great opportunity to resign Smart.
Yes, defense first point guard is the most replaceable position, BUT Smart is 3 years into his NBA career. That's 3 years of playing competitive NBA basketball. While the statistics aren't bearing out his improvement you can see in his game a lot of minor adjustments and improvements that are going to eventually add up.
It's not like he's a joke, he was just ALWAYS a long term project on offense. People who are tired of waiting now just made the mistake of overhyping his potential. If, and I mean IF, the Celtics can resign him at an all time low in what the league accepts as his value and "potential" I'm all for it. Guys like Smart find ways to stay relevant in the NBA, maybe his offense won't bloom until he can't take over games defensively anymore, but at some point it will and suddenly you'll have a good defensive guard with strong passing skills and some offense who has spent half a decade under the best coach in the NBA.