Yes, you sum up those virtues and vices very aptly. And I like the end-of-school party image, too. There's quite a case for saying that most of those characters didn't really need to be there from a plot perspective, and that having so many robbed each of them of the chance to experience any very significant character moments. But it was damned good fun, and I'm glad that amongst all that, RTD chose to keep the real star role for Donna.

Runaway Bride I would recommend catching if you can. Like the other two Christmas specials, it leans more towards Big! Action! Adventure! than some of the regular episodes, and lets go of some of their subtlety and careful craftsmanship in the process. But it's pretty good stuff, and will be especially interesting for you now, seeing it with the knowledge of what Donna becomes later.

As for your last line - aw, bless you! Do not fear, though - there is still much Classic Who for me to get through. :-)