Anyways, I'd consider insulating the floor (between the joists), and 'closing' off the vents until Spring. Since the ground around there is frozen pretty well during Winter, you'd open the vents once the ground IN THE CRAWLSPACE begins to thaw. AT that time, some moisture escapes from under the vapor barrier and you want it vented.
The insulation should have a vapor barrier on one side, such as Kraft-sided Insulation. The Kraft side goes towards the WARM FLOOR; NOT towards the ground. Don't go 'stuffing' it between the joists. It should be loose and luff, yet the Kraft should be snug up against the floor above. DON'T add any more plastic or anything in this job. To keep the insulation from falling down, you can either staple up some nylon string or chicken wire to keep the insulation from falling down. It will settle since it is simply in a 'cavity' (between the joists.) I don't like using those 'wires' that you rig between the joists to hold up insulation. If you can, spray some LOW-level expanding foam in any gaps under the floor. This will do wonders! ANd be SURE your piping is insulated and wrapped. 'Cut' the insulation as you need to fit around ducts and piping. Again, if you compress or stuff the insulation where you want insulation to 'work', you'll lower its R-value.
Now, at the same time, ask around up there what folks normally do in Winter (or year 'round) when it comes to crawlspaces. I know you've gotten mixed answers but ask why. Maybe someone's logic isn't right. Maybe one is talking about above vs. below crawls. Maybe BOTH solutions work.