I primarily use Spotify daily while in my car because I am a Marketing Rep which requires my 9-5 is strictly behind the wheel. I've completely replaced my iPod with Spotify but I find it's hard to "Star" a song while on the road. I use my Star folder as a way to eventually organize those songs into my subfolders.
I'm sure you know the way to Star a song already so I won't delve into those details but there is definite room to add a "Star" button by moving the "Last Song - Play - Next Song" buttons more to the left/right and placing the button there.
This idea has been submitted more than 1 year ago but unfortunately hasn't gained enough kudos during that time (10 kudos/year). In order to keep an overview of the active ideas in this forum, this idea will be closed for now. Note that this does not mean the idea has been declined by Spotify.
Please feel free to re-post this idea if you still feel you want this implemented. With a little change in presentation, maybe this time it will gain the necessary support from the community.