You should add ads on the mobile version whenever someone starts or loads a new game, and add a option to disable it. That should give you a little income and i'd gladly watch those ads to show my support!
That would just be annoying, and might get the game lower ratings. Sure, ads do generate income, but as this is meant to be something to play without a lot of annoyance, I do not feel the need for that. (At least according to me.)