From my understanding, whenever save states change in newer mame versions you risk your saved states being unusable and therefore you lose your high scores. Plus it only supports a relatively small set of games. If saving high scores is your goal, it's better to compile your own mame using the hiscore diff, and hiscore.dat.
True, but if you have MAME set up in your cab why would you update the version?
The same reason why there 'are' updated MAME versions released. Improvments, new games, bug fixes, new functionality, more accuracy (like in eliminating samples), etc. etc.
Also, if you are like me, you are anal in wanting the 'latest' and 'greatest' of everything...even if it might not be better than a previous version...I have that OCD issue where I have to have the highest number in a build...125 is higher than 124...125u1 is a little higher than 125....
And the last reason for me is if I don't upgrade, my cab starts to become untouched. I 'tinker' more than play.