Every time you upgrade MAME you need to upgrade the ROMs also.
That's an exaggeration. More like "Every time you upgrade MAME you also need to check and see if any of the romsets you use were also upgraded."
Only about 1% of the romsets change between major versions. Also, a single game might be updated multiple times over multiple mame versions; IOW, if a romset changed recently, it has a higher chance of changing in the near future (because it's being actively worked on). This also means that if you jump, say, 10 versions of mame, you'll probably have
less than 10% of the romsets need to be changed. (I'm talking generally, with rounding, so don't use these these as hard fact, always true, numbers; but they're okay guidelines.)