I dunno know Ernie, if luggage on a rear rack is a concern for gas mileage, I would think that driving with the top down would be just as bad, perhaps worse, for mileage. It's been 7 years now and I have yet to drive my speedy with the top up. I justify this by observing that all my instruments are metric, and kilometers per gallon is just a bit of bother. I put in a 15 gallon tank and drive.
As my ex-roomate, with a very large engine in his 55 Chevy, used to say in response to gas mileage questions, "whenever she need gas, I go fill her up!"
And the beat rolls on, and on, and on - thank you Cher!