@Pike: Thanks for pointing that out. I will take care and probably just have a disk swap, so I can go back to old install if something goes wrong. Do you know of specific forum threads about problems with 32bit backup on x64 installation?
I found this Transition from i586 to x64 hardware and How to switch from i586 to x64 platform which indicate that transition to x64 with backup from 32bit might work smoothly.
I’m also not using many addons.