I'm in the double digit gigabyte range as well and I truely feel you pain. WMP has been a pain since forever, even me, as a devoted Windows user I gave it up long ago.

However, if you are on W7 or XP MCE you should try giving Windos Media Center a go. It doesn't retag anything by default, instead relies on the library system for reindexing and grouping. I'm quite happy with it, it's quite nice except for a few thing (more weight than Winamp, e.g.). It does have a finished feel, however, and has the advantage of using index database and metadata to maintain its grip on reality. It also lives with user's idea of a playlist.

For lightweight, I recommend WA for audio (or foobar) and Media Player Classic - Home Cinema for video. Its ability to configure keys is priceless for remotes and CLI use.