^ I just rewatched it and enjoyed it much more than I remembered! Although, it's true that they don't interact much.
But, that's the execution of the idea. It doesn't have to be terrible and, in a new story, 2 Doctors could interact.
Just saying that seems to be a plausible solution for getting a classic Doctor in a story near the anniversary, not increasing the budget, yet still making the anniversary about looking forward.