I find that VBL can greatly increase my warmth and/or perception of warmth. I think it's particularly helpful for feet; as a day (or night) goes on, my feet and the insulation around them start to feel a bit damp, but feet are still cold... Evaporative heat loss happens. Feet are one of the sweatiest parts of your body, lots of "opportunity" for evaporative heat loss. Toss on a pair of VBL socks, insulation over them, and the insulation stays dry. Feet might be a bit damp, but totally warm... no evaporative heat loss and a more humid environment. No insulation degradation. I've found that my feet stay much warmer during a day in boots this way, too, as my liners don't get soaked. Bitter cold, latex exam gloves go under insulating gloves/mitts, for the same reasons.
And there's the old saying, already mentioned in ways: "If your feet are cold, put on a hat."