As an experiment for the upcoming New Stable (Wheezy) I did the following:
Took the latest LMDE MATE/Cinnamon spin and changed all the sources to Wheezy, removed the Mint source, installed Xfce 4.8 and ran updates. apt-get choked on the updates, so I ran aptitude update/upgrade and it took care of things pretty well. I still had about 30 updates showing in the update manager, most of those were MATE/Cinnamon related, so I used synaptic to remove MATE and Cinnamon and related files, and was eventually able to finish running the updates with the update manager. The result is not very Minty, it does have the mdm login manager and I kept Mint's icon theme. This install should be good right into the next Debian Stable, I can't see any reason for anything to break at this point though I wouldn't place a bet on it
My thinking is that by installing a 'pure' desktop onto a LMDE spin and removing the Mint source and using straight Debian sources the OS should be fully Debian compatible. The disadvantage is that you lose some Minty flavor, but you have an easy to install and relatively painless Debian OS. I must add that using aptitude to run about 300 mb of updates was more than an hour process for me. I would not be interested in running Testing/Wheezy sources except for the fact Wheezy is in freeze now as the upcoming new Debian Stable.
I'm not recommending anything here just pointing out what's possible