I picked up a Yamaha 12-string at a Flea Market - traded a beat up old Pakistani flintlock musket for it, actually. I used it as a twelver for a while, but got tired of spending free weekends tuning the blasted thing. A dozenplucker sounds lovely IF and WHEN it is in tune, but the harmonics go all to Chicago in a duffle-bag if it's even a little tad "out". And not all music is suited to the distinctive sound of the 12S either; particularly the traditional old mouldy stuff that I seem to gravitate to.

So I ended up stringing it with the 6 basic strings, and leaving the "doubles" off. I didn't change the nut; didn't have to.
This gives me the wide fingerboard which is highly conducive to the sort of fingerpicking I do, yet still sounds fine on the rare occasions I want to strum.

The Yamaha is built like a British Frigate of the Line, as most 12Ss are in order to withstand the 700-some pounds of tension that those 12 steel strings put on the neck. But the tone and clarity of it is quite nice, in my opinion. I use it for Nursing Home gigs and such where I want to put some sound out without distorting the pitch or clarity, and save the gut-strung Parlor guitar for around the campfire or "Living History" presentations at school.
It's funny that when I've been playing the Yamaha, it takes me a while to get used to the comparitively tiny fretboard of the old "Parlor".

The 1 & 7/8" plastic nut on my Yamaha broke off on the bass end recently, and no one seems to have the right size to replace it.
So I've got a couple of pork ribs up on the shed roof waiting for the "little people" to eat off the residual tissue so I can whittle me up a new nut. Bone makes pretty good tuning machine handles and nuts, actually. You can turn head pins and end pegs out of it too, in a pinch. I suppose deer antler would serve as well.

Keep an eye out for good used 12-stringers; there are deals to be had out there. A lot of folks seem to get them and give up on trying to tune or play 'em after a while and stash em in the closet somewhere (sort of like excersize equipment) for years, after which they finally sell them to make room for new junk, or move and don't want to pay or bother to take it along.   Mine looked as if it had hardly ever been played when I got it, but the case was disintegrating from age and dry-rot. As long as they were not stored in an attic or barn where heat, dampness, or critters got to 'em, they generally keep pretty well. If they were put away strung especially, check the neck for warpage before you puts your money down. Also check for delamination or glue joint failure anywhere. An instrument that's been cooked in a vehicle or attic will usually be coming apart somewhere. Fixable sometimes, but potentially expensive.

HTH - UJ