how much crucial plot and character development takes place in the gap between "The Doctor Dances" and "Boom Town".

I know... if you want my take, check out "The Sins of Adam" on the same subject.

I agree about the hinting. It adds a depth and three-dimensionality to the characters. Crackfic doesn't need it, but other stories are richer for it, including stories that have plenty of humor as well.