You appear to have conveniently left out John Robertson and Steve Paterson from your list and Brewster Mk1 was a success in that it established us as a Premiership side.
I've always felt that some of our best appointments have been with young, ambitious hungry managers with no link to the club. John Robertson, Brewster, Paterson all did well before moving on and earning the club significant compensation. Charlie and Foran seemed the easy appointment and neither really seemed to want to be manager at that point.
If we were to go down the road of a young outsider again what about someone like Calum Davidson? I've noticed he's been added to the Scotland setup (not in itself an endorsement) but by all accounts he's a very significant part of what Tommy Wright does.