We just got back from holiday in the UK(even though it's summer there it wasn't exactly warm
: )and my DH and I were having this EXACT same debate...
DS got VERY VERY sick- the first time he's ever had a fever, cold etc and we had him at the NHS doctors offices 3 times.
I asked the ped. about this- as my DH was PARANOID about having DS wrapped up in about 15 layers of clothes and blankets, even when he was sweating...it drives me CRAZY because I also am generally warmer than most-and HATE having too many blankets on me.. anyway-
The doc said it IS an old wives' tale. "colds" are caused by VIRUSES that get into the cells in your nose and breed causing symptoms; runny nose, coughing, sneezing etc. And keeping a baby too tightly bundled up when they are sick is generally not a good idea because it can make them uncomfortable (hot and sweaty)
Obviously you would use common sense and not send them outside in just a nappy or anything, but apparently wrapping up warmly does not prevent or help "cure" a cold.