Bobby Smith played more playoff games during the '80's than any other guy in the league (including all those Islander and Oiler greats), and he was a major offensive contributor during a bunch of his teams' playoff runs during those years.
Just as a quick example: during his first two playoffs...
1980: led Minnesota with 13 assists, including 7 in the 1st round sweep of the Leafs, and a huge one late in Game 7 against the Habs
1981: led Minnesota with 17 assists, including 8 in the semifinals against the Flames
He also finished his career with over 60 playoff goals, which is pretty darn impressive. Aside from Claude Lemieux and Esa Tikannen, all of the Hall-eligible players who had more goals in the playoffs than he did are, in fact, in the Hall.
I think his playoff accomplishments (if anything) would be THE major talking point when entertaining the idea of him being inducted. That said, I personally don't think his case is necessarily all that strong.