Really, extending trains on poorly maintained or abandoned track is quite ridiculous. But there's an opportunity - especially if Barrie moves the bus terminal to Allandale - for a nice tourism entrepot, with buses taking on passengers headed to Midland/Penetang (Martyrs' Shrine/Ste Marie, Discovery Harbour/beaches), Wasaga, Collingwood/Thornbury, Orillia, and the casino. At Allandale itself, it might be smart for Barrie to zone for some hotel and event space - there's a pretty good network of waterfront parks right there.
I would love to see a return of some of the pre-war summer resort culture in Ontario, when cityfolk would board trains, boats, and coach buses to places like Wasaga, Port Dalhousie, Gravenhurst (and onto boats plying the Muskoka Lakes), either to vacation homes, to resort hotels, or just day trips. Allandale could be that new gateway. I could really see this as I think the era of cheap airfares has peaked.