Ok I got really crazy tonight after work, and decided to upgrade all packages to those available in Karmic. I figured I had already done the major system stuff, so if I was careful and went slowly it could be done, and I was right. I now basically am running a Mint 7 / Karmic Koala ba$tard child. I'd imagine this is pretty close to what Mint 8 will be.
I did have a couple of hiccups, including having to purge and re-install ALSA. I also encountered a bug that's new in Karmic:
compiz --replace fails to kill metacity, resulting in cpu overloadhttps://bugs.launchpad.net/ubuntu/+source/metacity/+bug/389686
That had me going nuts for about an hour. Other than that everything worked out great.