You can but a few questions/comments:
1. Why update?
2. It'll be called MameUI now (to avoid confusion of 32 and 64 bit versions of MameUI with Mame32)
3. There was a change in Mame's programming around .104 or .106 so if you are running an older PC, you may find some games that ran fine before, will have issues with a new version of Mame. FYI.
If there are games added that you want to play, it may be worth updating. If not, I'd say stick with your current version.
You can always run multiple versions of Mame on your computer too. So if you want to play some newer games, you download Mame for those but use your old version of Mame32 for the "regular" games you've been playing. Depending on your comfort level on your PC, this may be relatively easy to do.