As long as they are well written, I'll take any multi-doc story. And if they are well written, well, then there aren't too many of them.
While I agree Dimensions in Time stank, tho it had an interesting idea .. sadly not much of a thread to follow, but an interesting idea - I disagree about the Two Doctors. It's my favorite 6th Doctor story, and the first one where I saw him do likable things, care about a companion more than a guilt reflex, and also the first time I saw the 2nd Doctor really strut his stuff and show off his comic genius. I love the Andregon(sp) Doctor scene, strolling off to town, arm in arm. After that I was more interested in finding 2nd Doctor stories and viewing them.
I imagine a good 11 Doctor story will do the same for a lot of the newer fans, give them something fun about less familiar Doctors and interest them in finding more old eps. The Ten Doctors story certainly did that for a considerable amount of readers, and while it may have started out as indulgent fandom, it quickly grew into an amazing story that gripped the reader and had more depth and twists than many episodes. With lots of indulgent fandom stuff thrown in, but that was just the icing on a well baked dessert.