I'm no expert, but I'd think it's worth doing, especially if you have anyone in the house with allergies or health conditions that are affected to mold. We had a huge mold problem in our basement earlier this summer (due to groundwater seeping in slowly through the walls. No leaks, no floods, just high humidity over a long period of time), and are having the entire basement redone. The mold remediation contractor found a lot of mold hidden underneath the carpet, since it stays perpetually damp, and there's plenty of "food" for the mold. I read an article that said carpet should only be installed in the basement if there's adequate "subflooring" or "underflooring" installed. Carpet laid directly onto the concrete will almost inevitably result in mold and the musty basement smell. For what it's worth, we've decided to do away with carpet entirely, and are looking into a waterproof vinyl floor.

Here's what the Building Science Consortium says about double vapour barriers: "The main problem with a double vapor barrier wall is that it cannot dry to either the inside or the outside should it ever get wet. In addition, it requires a perfect air barrier on the interior to prevent warm interior air from contacting and condensing on the cold foundation wall where it may be trapped. This type of construction should be avoided." Even the University of Minnesota study notes that in a basement without an internal vapour barrier, a dehumidifier would prevent excessive water vapour problems. Yet time after time, I come across musty basements that would have been fine if the owners had only bothered to invest $200-$250 in a portable dehumidifer and $50 a year in electrical charges. (I was just at a customer's home today. Sure enough, the dehumidifier I bought and hooked up to run continuously was stuffed in a corner of the basement.) I've used glue-down carpet for years in basements with absolutely no problem. But only low-pile with a jute backing that doesn't trap water vapour. Only in new homes and only with mechanical dehumidification. Here is a link that might be useful: Basement Insulation Systems

My first concern would be the water in the underslab gravel. Standing water there can indicate abnormal water inflow, a high water table, blocked or no drainage or even not enough gravel to hold the water until it drains off (there should be at least 4-5 inches.) The existing weepers should be connected to a drain or outflow somewhere. If not, they serve no purpose. A sump pump is designed for placement in a sump pit, which can be connected to under-floor drains and/or weeping tiles. XPS (extruded polystyrene) is neither dampproofing nor waterproofing. It is insulation that is not affected by the moisture in a basement. So don't expect it to stop water flow. Laminate on floor If you use XPS on the floor as insulation, you will need one or two layers of plywood over it, followed by electrical radiant heating and the laminate. Only use laminate warrantied for basement use and which is compatible with radiant heating; check that the radiant can be used under laminate.

Could the weeping be condensation and not a wet floor. If the floor was wet, wouldn't the carpet you pulled up be kind of moldy and damp? Have you tried the moisture test? You take a piece of polypropylene plastic and tape in down with tape so it is well sealed. You leave it for at least 24-48 hours. You can google "moisture teat on concrete slab" for further details.