For cabs, I suggest upgrading only as really truly needed, and only for specific games if your FE can do multiple versions of mame out of sight, rather than the whole thing. Then you can spend more time playing rather than updating mame, and patching zip file, and setting up. (FWIW, ajax rom set changed in 0.128u4.)
On my desktop, OTOH, I update mame to each minor release, but don't touch any rom set until I try to play one that broke, and I only update that one. Then when something "big" happens that I want on my cab and tested fine on my desktop, I can transfer everything from my desktop to my cab, and be able to play it as soon as the transfer is finished.