There is an experimental Picard plugin that will associate a Recording with the earliest Release date of any Releases it appears on. So if a Recording appears on a 1979 album, a 1998 CD anthology, and a 2015 iTunes/Amazon/etc. best-of, that plugin should set the “ORIGINALRELEASEDATE” (or whatever the tag is) to 1979, regardless of which of these the Recording is actually from.
Maybe give that a try and see if that works for you? (Of course, you’ll have to use a player that actually understands this tag too. Also, you may have to look into merging some Recordings as well, but that’s a discussion for another topic if you need help with that. :))
I don’t know anything about that plugin. Some players have the ability to fetch lyrics for you, so you may want to look into that. beets also has a more fleshed out lyrics plugin. You can also write your own lyrics plugin and contribute that to Picard—I’m sure others would like such a plugin too. 