Nice headlights, in most situations I'd say it wouldn't make much of a difference. But looking at the current set up you have, those lights will look way better and I think have a fair impact on your fuel economy. Good for you.
If you're going to do a coroplast bed cover, you may want to consider using some 1x2 for support, I'd say every 12-18" across the bed. You may want to consider raising it up as well with something like 2x4's around the top rim of the bed, I know I've seen a chart somewhere that shows the taller the bed, the better the mileage. It would be cheap and easy to do and would give you 3.5 inches more dry cargo height.