[rkcarguy]

I think this could be done to honda vtec engines with good results, as they have separate low cam lobes but shared high cam lobes. The only downside would be a bit of a flat spot between the econo-mode and high vtec as the flow died off before the switch point.
I don't agree with changing engines to Atkinson design, warm air intakes, etc. All that does is limit your *availiable* horsepower and make your car slow.
Aero, gearing, fuel/air mixture, and cam profiles that make the most torque at low rpm(and gearing to compliment) for freeway cruising are where the gains are found.