I recently removed an app from the store; it had only a few thousand users, and made no significant revenue. It felt good to not have to worry about it anymore.
So my suggestion is: Shut it down. Write a short goodbye email to your customers explaining why you are shutting down, then remove it from the App Stores and turn off your servers.
A side project will always take some space in your mind and distract you. If you see no future for a project, there's no point to keep it alive. You built a nice thing, but it seems it is not comercially feasible. Stop, and concentrate on the next thing.
So my suggestion is: Shut it down. Write a short goodbye email to your customers explaining why you are shutting down, then remove it from the App Stores and turn off your servers.
A side project will always take some space in your mind and distract you. If you see no future for a project, there's no point to keep it alive. You built a nice thing, but it seems it is not comercially feasible. Stop, and concentrate on the next thing.