I see this issue has been discussed before
https://discussions.apple.com/thread/2648843?start=0&tstart=0
But still no real answer to the question of how to import multiple playlists in one go (other than the not so helpful advice of don't use playlists).
Mix albums with multiple artists can play havoc with a library, particularly when viewing on an iPhone. In the 'Artists' view, the artist with one track on a mix album will show up. You then have to sift through many artists to get to who you want, many of whom you never even realise existed on your collection (please dont point this out as a 'feature'). 'Album' view on the other hand restricts your search by albumn name rather than artist name, which is not always ideal.
Also then when you're on a long drive, you may want to set a whole collections of albums off in one go so you don't have to fiddle with the phone while driving.
Playlists offer a way around many of these issues, and it sounds like if you lose your playlists then iTunes makes it difficult to recover. Also it used to be much easier to sync playlists between iTunes and iPhone, rather than sync artist/album combinations (I've not used iTunes since the hard drive on my MBP crashed (6 months ago), so it may have improved).