It's significant ... check your gas mileage with/without to see the drain. In my wife's ATX she gets around 500km/tank with air ... without air we were getting closer to 600km/tank ... this was mostly highway.
Personally I find people like your monster=in=law (nice term bty) to just be noisey little whiners who can't live outside of a 'pre-conditioned' environment ... I grew with no AC and only got it on the Tour and never had it in my home until I moved in with the (now) wife. Doesn't bother me too much and I never needs so I'm happy ... damn, better stop as this is turning into a rant!
