Windows 7 XP mode

is it worth upgrading to Windows 7 Professional/Ultimate for XP mode?

In my opinion, for everyday kinds of people, no.

For XP Mode? No. XP Mode requires a CPU that supports hardware virtualization (which not every CPU does, even today) + even more RAM (on the order of an additional 1 to 2 GB) IN ADDITION TO what is needed for Windows 7 to begin with. Not worth it, especially if you can't support it to begin with. Now if you just wanted the other features offered by the Professional and Ultimate versions, that's all fine and dandy.