Not writing has been a weird place for me. I think about the act of writing during most of my free time now, but my muse has been strangely silent. I think about the fact that I am close to finishing and know I have a few scenes left to put together, but there is no spark. This leads me to believe that writing, the actual act of putting pen to paper or fingers to keyboard actually sparks the muse and keeps the creative juices flowing. The more you write the more these creative pathways open up and tap into that right side of the brain and free the little fireflies of imagination.
I have often heard people ask writers where they get their ideas. I've had people ask me that very question, but from everything I've read or every time I talk to other writers they all say the same thing, ideas are the easy part. Writing seems to snap into place a cable in your mind that lets the creative side of your brain be heard over all the stuff the left side of the brain is dealing with on a daily basis, trying to get you through your work day. (unless you are an artist of some sort of course).
The answer to where do the ideas come from is, they come from the writer's brain. It's almost like a muscle though, it needs to be exercised. You need to read...a lot! You need to actually write, not just think about writing or talk about writing. You need to actually do it! World building is fun and is a nice creative outlet, but don't stop there. Create some characters and give them a problem to solve and write some scenes. You will be surprised what your mind will come up with if you give it a chance. The more you do this the more other ideas will pop into your head, stuff you never dreamed of. Then you get to connect the dots or rearrange the puzzle pieces to make a story outline. It's really that easy to get started.
Good luck with your writing!