I keep my eye out for a Star Wars, as soon as I can find one used or bargain binned for the right price I'll grab it. I have thought about a Big Buck but I hear they are kinda crap. I think one or two is ok they are an easy starting point and can introduce people to modding and the arcade hobby in general. I have a MAME cabinet and for me that is the way to go. 1ups just seem like a novelty item that is going the wrong direction price wise. I can't imagine the guys that buy them all, that is one expensive and generally kinda crappy arcade.
The golden rule for MAME is do not put any games on you don't play. These setups with 1000s of just shitty games and countless clones, just way too much hassle.