other than compatibility, there are definitely advantages to upgrading.
For example, I noticed I was able to play the "beta" versions of some 3D VS Fight games with a more accurate speed, most notably Mace -The Dark Age. A "beta" for me is when you get a warning "the audio or video is not 100% accurate" before the title screen. This might be due to the faster CPU or "fully enabled" OpenGL drivers of my relatively recent Radeon GPU.
Also, I don't really get how newer MAME binaries can be slower. Are you talking about the GUI or the games themselves ? It seems to me MAME is throttled when a game in launched, so I am surprised to read it feels slower for you. Also, if some games won't work, there must be some discrepancy between your version of MAME and the roms.
As for HD space, it's easy to get rid of most of the CHDs after you downloaded them, simply replace the ones you don't need (bowling, horse racing variants...) by a .txt file. Personally, I burnt them onto DVD-Rs and kept a few cool "action point & shoot" games like Area 51. Oh, by the way you wouldn't want to miss Street Fighter III
, do you ?
Finally, I was under the impression 0.119 was a major update, since "plete" collections were released at the same time, and exotic MAME binaries started to flourish. When playing an old 2D game it's nice to have the bezels surrounding the screen, and these enhancements take vitually no HD space.
Oh, but I am no MAME specialist, like some of you I prefer to avoid updating too often... I simply consider it's rewarding to slowly build one's collection. However it seems lotsa MAME resources are being re-allocated these days, so beware of broken links.
This said, there are some evolutions goin' on apparently : The CHDs are getting a hash signature and Daphne Laserdiscs (Dragon's Lair) are being incorporated into MAME (so if you don't need them : more HD space spared).