Your mission, if you choose to accept it,

[mmcirvin]

is to hack the best crude approximation of the feature I just suggested onto the existing iTunes using an AppleScript. You couldn't come that close with the tools available, but maybe you could do something useful. Try using the star ratings as your metadata field; obviously they don't have the float precision I talked about, being integers from zero to five, but it might be worth seeing how well you can do. The script would assign a star rating to everything. If the pre-existing rating is zero, the script would generate a rating from one to five from the play count and time last played. Otherwise, it could make use of the pre-existing rating and time last played. Details are up to you.

I might try it myself.