Is there an automated way of downloading your whole collection to your HDD?
Right now I have to delete the song/album then manually click down to redownload the 256 version.
I was doing the same thing, but then it hit me smart playlists!
Here's what I did.
Create a smart playlist with following conditions.
1.Bit Rate in range 96 to 254 kbps.
2. iCloud status is matched.
Then you delete the songs. After that I created another smart playlist
1.Bit Rate is 256 kbps.
2. iCloud status is matched.
First playlist shows all of the matched songs in your library between 96 and 254 kbps.
Second playlist have will this ->

You can do the same thing to all your purchased songs that are still 128 kbps. Just switch iCloud status from matched to purchased.