O.K. So this might not be right guys, but here was my thinking on the fiberglass and vapor barrier.
I know you need the v.b. on the top side, cause the air in the house is warmer and thus can hold more water vapor. My thinking was that this would be different than insulating an exterior stud wall. Here the insulation is on the underside of the main floor and you've got all that humidity on the other side of the insulation too. My thoughts were to prevent all that humidity in the cellar from penetrating into the fiberglass by sealing it off from below as well as above. I also see the potential for trapping moisture in the batting between the two layers and that's one reason for thinking the spray on stuff is just a better solution: humidity isn't going to get in from either side. Another reason is that the owner likely doesn't want to pull up the floor boards from the joists to lay the v.b. in a flat plane between the subfloor and the joists. Weaving it from below from joist bay to joist bay over and over is a pain and you can't be certain of avoiding little punctures in places. With rigid foam boards, you just can't fill up all the little spaces; you have gaps no matter what. With the spray on stuff, it expands into every little hole and crack giving an airtight seal in every spot. No air goes through, no humidity goes through, no tiny uninsulated spots, no tacking v.b. from below, no pushing fiberglass straight up while gravity pulls it straight back towards your eyes and nose!
BTW, when you "sistered" those joists, did you perchance use pressure treated lumber and use a water sealer on all sides (especially the end grains) before bolting them? If not, I'd slop a ton of that copper napthenate (sp?) preservative on it before proceeding with anything that'll cover them up. Protect your eyes, skin, and lungs when you apply the stuff-it's toxic. I'm not sure if I'd put a water sealer on the sides now though, because you probably can't get to the end grain to seal them. If you sealed the sides but not the ends, humidity could wick straight from the ends through the center and trap moisture in the center and maybe accelerate any dry rot in the center instead of slowing it. If there's ANY way to get some of the copper solution to the end grains on those joists, though, I'd surely try.
Most of the stuff Tommy does on the "Ask This Old House" isn't really on "Old" houses. I'd bet he'd love to come do this job on your gem of an old house with all these issues with the joists, etc. How'se that verse go, "Ask, and it shall be given. Seek and ye shall find. Knock and the door shall be opened unto you." You don't have anything to lose, the key word is ASK. Tell him a bunch of tractorhead fans are rooting for him.