All the developers in the world can only have so many ideas, and they'll only do as you're told. To get ideas for new things to do, you don't need developers, you need... a userbase.
Provide somewhere, like a forum on your product's website, where your product's community can suggest new features, report bugs, and express opinions about the project. These are the people who'll give you ideas, because these are the people who use the thing - listen to them, because they've got experience. They'll tell you what bugs bug them the most (pun all too much intended); they'll tell you what your software needs, they'll tell you how to improve what it already has.
That should give your developers enough to be getting on with. If they give you lots of ideas, then you might want some more devs to keep up with them.