Assuming your /home partition only contains data and configuration information, the architecture of the system reading it is irrelevant. In theory it should make no difference. That said, I would certainly backup when the time comes, because you never know what the installation process might do to existing data, and depending whether the 64-bit is a direct equivalent of the 32-bit or not, there might be a recommendation to start with a clean /home.
We will have to wait and see.