It's hard to say, but if its true that you can get 1.8% change in h.p. for every 10% change in air temp, I suppose there might be a corrosponding change in fuel mileage.
Whether that change is up or down, depends on what the median testing temps was for the engine and its rating.
But if for example, there was a 20 degree decrease in temps from before, that could be a 3.6% increase in h.p. and mileage from before. With mileage being an average of maybe 12 and a maximum of about 15, that's only an increase of about 1/2 mile to the gallon, so may not be as noticable. Even with a 50 degree change, you'd be hard pressed to see a 1 mpg difference.
I could also be completely wrong that there is any corrolation between the mpg and h.p. change with air temp...or...it could more, who knows.
Interesting thought, though.
I am thinking about pulling off the fender to get a better look at things and look at some options for ducting cooler air without a snorkle. Maybe remove the inner fender liner.