What're your goals? Thinking about what you really want out of side projects may help. It gets the blood pumping to think about building a project that is finally the one that makes you millions, but creating a highly profitable business is a very different set of skills to building the technical side of a side project.

I'm in a similar boat, you are doing FAR better than I ever have (many "plans that come to naught, or half a page of scribbled lines" over here), but lately I've not been too disappointed.

I stopped caring if I failed to complete a project once my initial burst of interest disappeared - usually as I'd learned what I wanted to learn and my curiosity was best directed elsewhere rather than slogging on with a project I'd lost interest in (plenty of those you can get paid for, this is supposed to be hobby time!)

The new skills I learn for fun have led onto new jobs, better ability to function at my day job, friendships, collaborations, a fun summer at ITP Camp in New York, etc.