Unless you have to.... then, be very careful and very aware that all may not go as planned.
For us, we did a wholesale migration from 4.5 to the latest 5.02. (at least 25 systems) We just never have a window where we're not in the middle of a project, and we REALLY wanted to use the multi-clip function. Yes, we had some shows in progress. Yes, we had some minor problems. However, by and large it went better than expected.
Some words of caution. You can always go forward (newer version) but never backwards (new to old). Once you make the change, don't plan on going back.
Save copies of your old project somewhere else if for some reason you need to revert. Read these boards. Pay attention to what people say about upgrades.
The word on this one is that it's pretty smooth. That isn't always the case.
Good luck.
Mark