I have a similar motivation problem. I tend to do just one at a time, and obsess over all sorts of little things; I still haven't finished any of the twelve or so kits on my shelf. I've been putting it off, and putting it off, and meanwhile the stockpile grows...By the time fall semester starts, all I have to show for my effort is an ugly (but functional) plywood spray booth in my bedroom window, a cluttered work area surrounding it, an unfinished model lying there collecting dust (which will have to be washed AGAIN for the umpteenth time
), and a $1000 balance on my credit card.
Be glad when you get done with your projects. When you're working, it's a satisfying experience, but it's even more satisfying having a handsome model that's completed.