The crawl space originally was such a huge mess!
The thin black plastic was not installed well to begin with, some of the neighborhood animals had gotten in there we think (the smell was NOT good), and water, and dirt made the space quite gross. We were very glad that we had decided to replace much of hte brocken and cracked rabbeted floor boards with plywood instead.
Once the subfloor was open it was far easier to remove the old plastic, add the new foundation elements needed (lots of them!), and install a new vapor barrier.
The new barrier is a 12mil, fiberglass mesh reinforced, multi-ply membrane that is taped at all the seams. It runs up the sides of the concrete stem walls in order to keep the moisture at a minimum in the crawl.
Not only does this make for a cleaner crawl space, but also a cleaner living space, and a place to potentially store some items. The original home had an above ground oil tank that we removed, and there is a nice concrete slab area in the center of the house.... perfect for some wine racks, maybe??