I know I'm a day late and a dollar short but...
I'm an avid collector of sewing machines. I use them, I love them, I've even been known to pet them. I own a 99-13, a 66 and a 201 Singer, and a 72 Monkey Ward and the Sears Big green ugly machine (it's from the 60's and it is UGLY). Of them all, 4 are electric, one is a treadle.
Usually unless the machine's been treated awful, the motors should be ok with a little repair at most. My 99-13 (it's a small version of the 66) is crappy, and while it does fine seams, it doesn't do strong seams. The original motor is still there, and it still works, and it was a motor on the outside. This is not the machine I use for anything but a quick rip through of a seam or two, and really, my other machines do it better. Since this is the smaller version of the machine I use the most, it is the one that I take for demos and classes, I usually french seam anyway, so the detail work is brought home and finished on the main one. It was my first machine I bought 15 years ago when I was 15.
The 201 is an internal motor and many sewing enthusiasts swear it's the best machine out there. I will admit, it does a variety of stitches, and it's fairly powerful.
TBGUM and Monkey Wards were gifts, and I seldom use them, they just don't do what I want.
My main machine is my treadle, non electric (it has a motor that was added later) and while it was leaky, the machine sat 25 years before I got it, and the first thing I did was pull it off. This is in a cabinet, and it's the type used in the old days that you see with the women in corsets.
I use Singers, I prefer Singers and the old machines, pre 1970's were awesome machines. I would run, far and fast, from a new singer. That said, my corsets are only sewn on my treadle. To me, an electric goes too fast to make the channels right http://waist-trainer.org/silk-floral-brocade-corset-review/, and the treadles seem to sew through anything with the right needle. I've made more then one machine get hot trying to make a corset or sew pvc. The treadle doesn't have those problems.
All that said, Elna makes the best machine out right now, and I hear many good things from people who sew not only corsets, but clothing as well.
I do know I can sew as fast on my treadle as I can on an electric, and I get much finer stitches (not to mention my buttonhole attachment works with it) and there is a built in side table that allows for the old clothing with yards and yards of material to be sewn.
There are also other concerns about feed dogs, shanks, attachments, feet, bobbins, and the type of sewing (ie. do you need zig zig stitching) to consider.