Dixie Deans and Tam Forsyth are the first players I remember going directly to the OF. It was more prevalent in those days. Bosman reduced the traffic in that direction, but they still have a habit of trying to pick up Scottish talent without often ever making use of them.
I think Turnbull is good enough to succeed anywhere, which is why I think he'd be better off outside of the SPFL. While I'm sure the money will be great and it will be nice to win an honour or two, I'm not sure playing against Livi and Accies for another few years will accelerate his development.