I have a 6100-based vectormame, a Tempest, and an Asteroids, and here is my take:
I am perfectly satisfied with the 6100, but that is mostly because my favorite games are the color vectors. Are they as sharp or bright as the vectors on the Asteroids? No, but they still look tons better than any CRT, LCD, etc., in my opinion. The color games, most of them, anyway, were designed for the lower-rez color monitors and so presumably didn't include detail that would be lost. In some of the b/w games, the objects are small enough to look a little funky on a 6100 (e.g., Solar Quest). I do, however, like having the simulated overlays for the B/W games, although there's really no way to recreate the stuff in Warrior, Armor Attack, etc., where the overlays had graphics in addition to color (Yeah, I know Warrior didn't technically have an "overlay," but you know what I mean). Yeah, Asteroids on a 6100 looks like

compared to the real thing, but that's why you get the real thing...

Sure, I've thought about building a dedicated b/w vectormame, but over time I found that I just don't play the b/w games enough and like to have "overlays" on the ones I do play. Just my 2 cents...
As FF recognizes, however, using an Amplifone would probably be the best overall solution, and I will do that as soon as I get around to fixing the one sitting on my bench, if I can...

I could be wrong, FF, but you seem to be leaning toward a b/w, as your preferences seem a little different than mine. And although I wouldn't be, you seem perfectly happy playing the color games on a PC monitor. Whichever way you go, you won't be sorry, but then, since you already have some vectors, you already know that.

The good news is that a b/w monitor should be a heck of a lot cheaper and more reliable to boot. I'd be interested in hearing about any practical overlay system you came up with.
Yeah, the sound can be a problem. I messed with it for quite a while before getting a PCI soundcard to work in DOS, and I'm still not sure what I did. I tried and tried, and suddenly I had sound and haven't touched any of the setup files since. I know my card is a SB, but I can't remeber the model number off the top of my head. Here's some general info, though:
http://www.mameworld.net/dosmame/setup.php