You know what - MAME is a miracle! The whole thing. I have never lost my feeling of wonder and amazement that it works at all - that we can play these games (almost) exactly as we did back in the day. I hope I never lose both my gratefulness, and amazement that it's possible at all.
For the record I play Mame on an i7 machine with an Nvidia 570 card and 16Gb of RAM. There are STILL games that are not really playable due to performance issues. However, my favorite games play perfectly.
Having said that, my system is not dedicated. With this much power I make Mame artwork, browse the net and so on. There's no shame in that. Maintaining old software and devices isn't as easy as more up-to-date equipment, it's that simple.
Buy the most you can! And when Mame developers go to that next level - as is the case with discrete soundboards - I'm all ready to go with them.