The upgrade process isn't that hard, especially if you are with Sprint.
1. If you've never done a ROM upgrade and you are upgrading to the new official Sprint ROM it's as simple as backing up your phone, downloading the update, connecting your phone (activesyn) and running the upgrade. It updates the ROM and the Radio (which is very important). This basically gives you GPS functionality and faster Data speeds (where it's available). There are other changes but they are minor.
2. Custom ROMs require a bit more work, but if you'd done step number 1 already, you are halfway there. You just have to follow the instructions listed in some of the various custom ROM threads. The added step is that you have to load
SPL 2.40-olipro. The confusion also might lie in the fact that there are quite a few custom ROMs available. Just spend some time reading and you can decide what one is best for you.
If you are NOT with Sprint it's a bit more complicated but not that hard. You have to first upgrade the Radio and then do a Custom ROM. I have Sprint so I don't know exactly what the process it... (any comments from non-Sprint ROM experts)
Bottom line, if you don't want of need GPS functionality then it's probably best to leave well enough alone... But IMHO, having a functional GPS on your phone is pretty nice.