Agreed. If the Eighth Doctor was doing something that thematically or directly ties into the Anniversary story, then fine. If it's just to do it for the sake of doing it, I'd be more let down than a pointless cameo in said story.
But IMO, most of the Doctor's regenerations are incidental to the story at hand - most of them could easily have been standard tales with the regeneration a slightly different ending to the usual result of the climactic peril he was in at the time (i.e. he dies instead of miraculously escaping). Doctors 2, 3, 6, 7, and 9 go out under circumstances that don't really affect the story at all, where 1 and 5 have minor effect on the plot IMO, especially compared to the drama-fest that was 10 going out. We *like* seeing a build-up to a regeneration, but rarely get it. However, we *love* seeing the aftermath of a new Doctor arriving, though plot-wise it NEVER has anything to do with how he got there in the first place.