I think Smart's ceiling is Iggy, especially as he improves his offense. He plays well when he plays within himself offensively and under control. I think he is worth 16m right now, and that is why he will probably be moved at the trade deadline.
Smart is not even close to Iggy as a player.
Iguodala in his prime was superior to Smart in literally every single aspect of the game - better defender, better passer, better rebounder, better scorer, better shooter, more athletic. Maybe you could make somewhat of an argument for Smart's defence, but IMHO Iggy was a superior player on that end too.
Iguodala was the 76ers go-to guy on offensive for a number of seasons there, and he was a borderline all-star for years. I don't think there is any chance that Smart will ever be that for a team.
Smart really is more like a Derek Fisher. He's a defensive minded guard who has decent (but not great) PG skills who can occasionally have an impact on the offensive end and has a tendency to have big moments in the clutch. I honestly find it hard to imagine Smart starting for many NBA teams given his major offensive limitations.