You can actually keep your /home partition intact with a new install. During the partitioning phase, you put a check in the box to format the / partition. Do not put a check in the box for your /home partition. You will get an all new / partition, and your /home will be right there ready to use. However, there are some hidden settings in your /home partition. They are nothing dangerous, but your personalizations are stored there. For example, if your Mint 5 install had "Elyssa" down by the menu, your Mint 6 will probably still say "Elyssa" even though it is not. These are minor things that can be fixed in a few minutes. Husse has written numerous posts on moving from one version to the next, so you should benefit from searching out and reading them.
Now, I have done the above method in the past with numerous other distros, and it works. However, what I have done for the past two years or so has been to copy my most important files to a flash drive (I have whittled down anything mission-critical to just a few hundred MB!). I then perform a complete clean-install with everything freshly formatted. I then drop my files and settings back in place. This only takes a few minutes. This method works best for me. Only you can decide what works best for you.
Husse also has suggestions for a separate data partition, and you might get some upgrading ideas from that. You can usually find some interesting items in the wiki. Good luck.