Ranking subdomain even possible?

I work for a franchisor which means we make a new website for every new owner of the franchise. The subdomain is the location of their business (i.e. boston.franchise.com). We currently run 34 websites and counting. Our PPC ads and local SEO is doing great but my boss wants us to start pumping out content more to get these sites higher in the organic search results.

Does anyone have experience ranking sub domains? It seems like everyone on here says don't do subdomain but we are well past that and just need to get them better organic, in-bound leads. The problem is doing SEO for 30+ websites seems rather impossible given how much work that actually entails.

If we go the content route, would the content have to be unique on each and every sun domain? Or could it be the same across the board. What are some good strategies given our unique business?

Appreciate any insight anyone can offer.