Hi Roger -
I'd skip the cold air intake: it's not going to improve mileage. It's more likely to lower it.
You're right to focus on aero mods, since your driving is primarily highway. If you haven't already, check the list of mods:
65+ Vehicle modifications for better fuel economy - EcoModder.com
Also, tuning the nut behind the wheel is a major factor:
100+ Hypermiling / ecodriving tips & tactics for better mpg - EcoModder.com
And instrumentation, like a ScanGauge or MPGuino is highly recommended.
Welcome to the forum!