Not sure how you figure there are "umpteen variants" in storing album art...maybe it's different for non-embedded art and I can't tell since all my art is embedded. For something like the Album Art->Cache folder it's a pretty simple scheme:
1) Each folder immediately within the Cache folder is named for your iTunes Library's ID; if your iTunes has seen more than one Library, there will be more than one folder;
2) Enclosed in your Library ID folder are 16 folders, named "00" thru "15" -- these correspond to the last hexadecimal digit of a track's Persistent ID (where hexA is 10, hexB is 11, etc.);
3) Enclosed within each of those folders are (up to) 16 more folders, "00" thru "15" -- these correspond to the second-to-last hex digit in a track's Persistent ID;
4) The final group of (up to) 16 nested folders represent the third-to-last hex digit in a track's Persistent ID; the pre-digested .itc art files are stored here.
So for a track with Persistent ID 1E8F5DD7B4F057C3 in my library ID C71236259DC2FEF7, the cached artwork is stored in: iTunes->Album Artwork->Cache->C71236259DC2FEF7->03->12->07-> C71236259DC2FEF7-1E8F5DD7B4F057C3.itc
I like this scheme -- it uses the file system as an index, rather than using an actual "database," so it's easy for humans to figure out. And it does a great job of distributing many thousands of files within a fairly compact tree in a manner that doesn't overload any particular folder.
For particulars on the .itc file format, let Google be your friend.
(Just a note -- starting your own thread is better than reviving a 6 1/2 year old thread ;-)