Stock wheel aerodynamics, wheel wieght and offset

I have an 08 Prius with the base wheels (15x6 with 45mm offset) I'm looking at getting a set of aftermarket wheels that are 15x6.5 with a 38mm offset. The weight of the wheels are approx. 14lbs. I'm wondering, will I suffer any negative side effects by going with these wheels? I'm not sure how big of a part aerodynamics plays a role when it comes to the stock wheels and I don't want to screw that up. I'm also not sure on the weight of the stock wheels, but I think it's 14lbs isn't it? The new wheels are going to be .5 inches wider, and the offset if going to change by 7mm toward the fender. Any input would be greatly appreciated. I just don't want to buy these and end up getting worse gas mileage.
Edit: just noticed I spelled "weight" wrong in the subject, not sure how to fix that...

 

That's right, forgot to add the extra mm to account for the width... Hmm, I'm really wondering how much aerodynamics will play a role...