I'm a rails dev too, last year I was making a mobile web app where I was concerned about frontend, so I started making a SPA in mithril.js and using Rails as the API.
Later I abandoned the SPA and went back to rails views, using turbolinks to make it fast. In reality rails + turbolinks is fast enough for most cases, and then I can sprinkle in extra javascript or use SPA on one or two pages as needed.
The reason I think it's almost better to avoid SPA + API approach is to keep the codebase simple and easier for one person to maintain.
Later I abandoned the SPA and went back to rails views, using turbolinks to make it fast. In reality rails + turbolinks is fast enough for most cases, and then I can sprinkle in extra javascript or use SPA on one or two pages as needed.
The reason I think it's almost better to avoid SPA + API approach is to keep the codebase simple and easier for one person to maintain.
https://www.youtube.com/watch?v=SWEts0rlezA http://masilotti.com/beermenus-and-turbolinks/