For the internal HDD, I got a bunch of spare USB thumb drives and put only one artist at a time on each drive and imported them individually. Renamed USB1, USB2, etc, automatically generated folders to the artist's name. Now at the root of the internal HDD, I have artist separation. If I want to change it up, now I can do it by artist, and not have to re-import another 12GiB. (though the music I put on the HDD is some of my all-time favorites, so I don't often switch it up).
For the USB in the console, I leave a 30GiB iPod in the console with tons of playlists. I also occasionally plug my iPhone in when it has some newer music I haven't had a change to sync to the iPod yet.
2011.5 E92 ///M3 Space Gray; Fox Red & Blk; 6MT; ZCP; ZCV; ZP2; ///M Performance Exhaust (sold)
2012 VW Jetta TDI (sold)
2002 Subaru WRX (sold)
The World in 35mm