Yes, all of the mods you posted will help. Only you can determine if they're worth your time.
As for costs, the challenge with improving the efficiency of an already efficient vehicle is you have to keep them as inexpensive as possible because the payback period is very long.
EG: simple coroplast boat tail:
Quote:
My personal results will no doubt be different from yours, but driving 50/50 highway/surface road I saw an 18% increase in mileage.
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From:
http://ecomodder.com/forum/showthrea...mpg-24999.html
I'm a little skeptical that % improvement would stand up to A-B-A testing at constant speed highway driving.