I just wanted to put in my two cents........This will pertain to many folks in here, no hard feelings or disrespect intended.
When people have a mario bros, popeye, donkey kong, donkey kong jr & donkey kong 3 all in a nice neat restored row it kills me since its the same cab, monitor & controls. Same goes for seeing a collection of the mortal Kombat cabs or a line of Neo Geo's......seriously? Even a galaga, pacman, burgertime & etc play in MAME on arcade controls via arcade monitors inside a big arcade cabinet....
How many damn PCB boards to you want to troubleshoot, how many cap kits do you want to do each year....how many control panels do you want to have printed up? Sounds like more work than play to me.
I love MAME because it allows the enthusiast to have space for pinball machines, a pool table, foosball, darts, theater area, bar, bathroom & hell maybe even a stormtrooper.
Some games must be dedicated: paperboy, 720, mechanized attack & etc but everything else is fine.
This hobby is not all about playing video games; at least it isn't for me, and probably a lot of other people. In fact, playing video games isn't even close to being the most exciting thing in the world to do.
There is the restoration aspect of it; which is something many people enjoy, in and of itself; and not just with arcade machines.
There is the collecting aspect of it. Collecting is also a hobby for some people, in and of itself. Three of the most common forms of collecting involve items that you don't do anything with at all, beyond looking at them (coins, stamps, trading cards). For collecting to be satisfying, you need to have tangible things to collect; like Atari cartridges/boxes/manuals rather than ROMs on a hard drive plus scans of the box and manual. The same thing applies to arcade machines.
Wanting a complete set of items which belong together is a natural progression/extension of collecting; whether it is a complete set of 1955 Topps baseball cards; a complete set of Activision Atari cartridges (even a complete-as-possible set of Atari cartridges would probably be arranged into subgroups by the collector); or; a complete set of Nintendo arcade machines.
Nintendo is a particularly appealing category because all of their cabinets either look alike or bear a strong family resemblance; as opposed to something like Atari where a Star Wars looks nothing like a Centipede, which looks nothing like a Missile Command, etc.
Then of course there is the sense of nostalgia, and anyone with a halfway decent memory remembers most everything about the arcade machine, not just the gameplay; and tend to be nostalgic for all aspects of the machine.
So if you're just in this hobby to play games, then build a MAME machine with forty-eleven thousand ROMs and you're done. For others there is a lot more to it than playing games, and only original dedicated machines can scratch the itch.