Just btw (and a little bump for your thread as well 
) I know musicbrainz ID’s look like clutter, but without them you will have a very inflexible set of files.
If in 20 years time you think “hmm actually it would be nice to have a genre and a sub genre for each file” (or someone develops an even better genre source that MB can tap into!), you’ll have to start all over again. With an MBID, change your settings in Picard, drag in the files, hit save, and you’re done.
I know it sounds like I’m pushing MB-specific tags on you, but I’ll risk it in case it saves someone a lot of work in future!
Good luck unsetting all the other tags, sorry I can’t be of more help there.
edit: 7 years later, here’s a link to the complete unset list, to help any one who finds this via search