Another small update: When legacy grub is installed, qemu can actually boot other partitions on the main drive you are running from. (Module kvm-intel may not be loaded automatically.)

Code:
sudo modprobe kvm && sudo modprobe kvm-intel
sudo qemu -machine accel=kvm -hda /dev/sda -hdb /dev/sdb -m 1024 &
If legacy grub is installed on /dev/hda, this will give you the grub boot menu, and you can use any alternative, except from the instance you are already running (if you booted that way), and there may be partition mounting conflicts. If you have a USB stick or USB external harddisk, they may also be mounted from the VM in the ordinary way when /dev/sdb is given on the command line. Doing purging and installs in the virtual machine is about as fast as directly, and much simpler and safer wrt testing etc.

There are quite a few packages eligible for upgrade in 7.0.3, but I don't think it is worthwhile (or even safe) to try to upgrade all of them. For me, it has worked well so far picking the possibly important ones (like aptitude and qemu).

Maybe it wasn't smart to install the 64-compatibility libs from unstable this time too, for the stripdeb.sh script crashed for some strange reason. Running the steps to strip libc6 (libc6_2.13-34_i386.deb) manually worked, though.