As an engineer, I can tell you the hype about weight is HIGHLY overrated.
There are two factors concerning weight:
1) Lifting it while climbing.
2) Accelerating it.
For just cruising down the road, weight it almost irrelevant. Aero drag is the primary force you have to overcome, followed by a significantly lower frictional force due to rolling resistance of tires, bearings, etc.
As far as rotating vs. non-rotating mass, rotating mass is only a factor (above non-rotating mass) during acceleration (and deceleration). So, it's really only significant for those who need sprint performance (racers). As far as climbing is concerned, lifting an extra pound on the wheels is no different from lifting an extra pound on the frame.
So, if you really want to improve your performance, don't eat that second taco and loss 10 lbs off the engine. The performance gain will be 10 times that of new wheels and will cost you nothing.
Dave