Smart Playlist to Gather Upgradeable iTunes Match Tracks
Macworld's Jason Snell describes in this article how to upgrade tracks with iTunes Match to 256kbps AACs. iTunes Match will allow you to re-download these types of files even if the matched tracks are lesser quality. To gather these lesser-quality matched-tracks together, Jason describes how to create a Smart Playlist with the correct criteria. I've created that Smart Playlist and exported it and have included it in a script which, when run, will add that Smart Playlist to your iTunes for you. Here is the direct download link. Just download and double-click the script; make sure iTunes is running. Be sure to read Jason's article to understand the rest of the details.