Stop iTunes from auto-playing after import

Check if really iTunes is causing this by opening a terminal and entering:

 pmset -g

If sleep is prevented by a process its ID is listed, like here:

 ...
 sleep      0 (imposed by 129)
 ...

Then check which process blocks going to sleep, in this example:

 ps -A | grep 129

   129 ??        37:39.06 /usr/sbin/coreaudiod

Then try killing (quitting) the process and check if you can send your computer to sleep, and if iTunes is still working. In this example it would be:

 sudo kill -3 129

Otherwise you could try re-installing iTunes, and/or repairing your file-premissions in Disk-Utility.

You can do it better by placing files to the folder ~/Music/iTunes/iTunes Media/Automatically Add to iTunes in Finder (or ~/Music/iTunes/iTunes Media/Automatically Add to iTunes.localized in Terminal.app) to be automatically added to iTunes without any third party program