Basement ceiling insulation (yea or nay?)

I MOVED INTO THIS HAOUSE 2 YEARS AGO, BUT IT IS 25 YEARS OLD..MY CRAWL SPACE HAS HEAVY GAUGE PLASTIC COVERING THE DIRT FLOOR..INSULATION IS BETWEEN THE RAFTERS..I WANT MORE INSULATION ...CAN I ADD ADDITIONAL ACROSS THE RAFTERS?..SHOULD I REMOVE WHAT IS THERS AND REPLACE IT?..DO I NEED ANOTHER VAPOR BARRIER ATTACHED TO THE FLOOR JOISTS?...THANKS..DAVE

I am in a bind. I put up a post a while ago describing a problem I have in my kitchen. We re-did the cabinets about 4 years ago and I noticed that the drain for the sink was going through 3 cabinets and into the wall. So, we ran the drain through the floor and capped the pipe in the wall. Well, we didnt patch the hole in the wall (about 1.5 x 1 foot) we put the cabinet infront of it. So, now there is condensation on the inside of the cabinet. I took out the cabinet and I saw some insulation sticking out of the wall, so I assumed that the whole wall was insulated. Nope. No Insulation, someone must have put it there when they did the kitchen before we did. I can put my whole arm up the wall and cant feel nothing but cold air. I hit a hole in the wall in the next joist cavity and the same thing, no insulation. My question is I want to patch the hole in the wall, should I stuff insulation in there? We might have insulation blown in in a few years so I dont want to have any problems. Or, should I just tape a 6mil. poly vapour barrier to what is already there (something that looks like tin foil on the warm side and a paper bag on the cold side) and put drywall over it. The plaster is about 1/2" thick so I can use drywall. The house is about 50 years old and none of the other areas in the house feel cold. They also don't have holes in the walls!;) thanks for your help!