I agree that there are ebbs and flows to my quilting juices. You can wait it out and give yourself a break to try something different. I also have had this happen with projects that are not turning out as I had hoped. I then just tell myself I will sit down for 15 minutes to make some kind of progress on it. Sometime along the way it is either finished or my mojo will return.
I like the idea of swapping UFOs with someone.