I recently lost all my playlist and also moved from 80k to 22k songs. So I started fresh, I am also interested in knowing how people do their playlist but I can tell you what I have done so far.
I use iTunes to arrange my songs and I also only use Smart playlist only. When I add a song, I make sure I update the tag to go in specific playlist.
I have a folder for genre and years and record pool. For example, Genre >Dance >2000s > here I have 2-3 smart playlist based on BPM but limited to 1k songs ( I had to split them for RB).
Genre >Dance >1990s-
Genre >Dance >2000s
Genre >Dance >2010s
For smaller lists like dubstep, deep house, Trance, etc I place it here:
Genre >Deep House
I just have to make sure w/e song I dump in my library has a year and a genre to go into a playlist. Anything song that has neither are placed in the "Rest" playlist rested in each folders.
Thus far, I find this style very successful in organizing my stuff. I do not need to drag and drop, it will go there based on the tag, just like a database file.
FYI, I am going that route simply because I am also currently taking an Oracle class (database program) so I find it fun to work that way.