Swearing by (or at) anything
Both the Mobile Maid and this D&M are extremely cool and capable machines. You've also proven your tenacity and skill at taking on some killer mechanical projects, so I think either would be workable in the bigger context.
That said...
I have found one golden rule in the world of vintage appliances: You can be screwed by anything. This is why I have two of everything. No matter how much an evening spent over the kitchen sink with Palmolive softens cuticles, it can't soften my rage.
I have spent countless evenings after dinner crawling under every dishwasher I've owned--KitchenAids, GEs, Thermadors, and of course, D&Ms. Many, many D&Ms. Everything has, at some point, leaked, shorted, thrown the pump seal, broken the detergent dispenser, or--my favorite--sheared off the wash impeller. This only happens in the middle of a load, of course, and as un-entertaining as it is with a portable (cue sound of screaming as machine gets pushed outside to be drained into the yard), it's far less so with a built-in.
I'm a relatively sane and somewhat normal person. I don't dump bags of gravel into the machines; I don't pre-wash my dishes, either. I don't get hit by lightning six times a day, and pianos don't usually fall on me, so I think my luck is par for the course. Still, I'm probably the only person in the neighborhood who has nut-drivers and silicone sealant in the kitchen drawer.
I usually go for vintage stuff, but I also research the parts scene first. It's all relative, but it helps me know what I'm getting into. The vintage v. modern debate is apples-and-oranges; you can get good performance from just about anything with the right loading and combination of other parameters. (Except that Tappan wet-tire-drum thing.) The real difference is repairability. Yes, the Internet is full of modern dishwashers with dead control boards, but you at least do have the option of getting a new one to repair it.
Neither the Mobile Maid nor this would be my choice for a daily driver, unless you were cool with hand-washing dishes when either one crapped the proverbial bed. Despite the great performance of these machines in the days when we had vintage Cascade, positively throbbing with phosphates and that great fragrance (can't someone bottle that?), and despite the fact that it's possible to find a way to get good performance now, keep in mind that we've fast-forwarded forty years (more like fifty for the Mobile Maid).
Parts are nearly nonexistent for the Mobile Maid, and all the stuff that breaks commonly on these D&Ms are the things that require long-distance phone calls to local appliance shops in distant lands to find, or forlorn wanderings through eBay. Working on the pump-guts of either of these after years of use is almost as much fun as skydiving from an airborne papercut convention into a salt mine, and I'd rate the Mobile Maid as about six times worse in that department. I've also had both machines do things like get NIB pump seals...and then leak a week later. The "new" parts are, sometimes, nearly as old as the machines, and they don't escape the throes of aging, either.
So...if you love it, get it--but I cringe when I suggest vintage-anything for a solo role. I've owned brands that were exalted for their reliability that died early on me, and machines that were supposed to be garbage that ran and held up beautifully.
But seriously, $250 for a used D&M? Bump the decimal one to the left.
