I used to think I HAD to finish one project before I could start another one - now I know better!
Like others I can get "tired" of the large ones by the time the top is done.
I hav found that if I mix some small projects in between the top making and the sandwiching/quilting of large projects I can enjoy all of the processes more.
Doll Quilt or Table Runner swaps are a great thing for the above.