Well in your situation, I would upgrade your hardware as you are intending to do, grab the latest versions of everything, mameui, roms, samples and anything else you would like screen-shots etc...
Keep your old mame/roms etc. in a separate folder for the time being, this will allow you to revert if you don't like the new versions. It will also allows you to migrate any settings to the new version in a non destructive manner.
There are plenty of excellent resources for downloading complete verified sets of everything, you wont have to hunt around to much. Just start off the downloads and you are set. Nothing to it really.
I cant imagine you wanting to revert once you have the new version configured.