UPDATED: Needle Drop v5.2
Needle Drop is an applet that plays each track in the selected iTunes playlist for a set time interval optionally starting at a set number of seconds into each track, beginning with the selected track.
This latest version adds the "Start fade at seconds" option, which is the number of seconds from the end of the full duration to start fading iTunes' volume for each track. Using the settings above, each track in a playlist would: 1) play for :30 seconds 2) starting at the :10 second mark, 3) begin fading at :24 seconds (30 - 6) and then 4) wait :03 before the next track begins.
Needle Drop is free (donation requested) and more details and download are on this page.