The problem is that it is not 17 to 17 = nothing like some are suggesting. The problem is which 17's. There are boat anchors out there that are meant to be pretty to look and nothing more and then there are the really light wheels that don't look so hot but are meant for driving. I am not as current as I would like to be in this since I haven't bought wheels etc since the 5th gen so I can't really give you models right now but I would suggest that you strip the rubber off one and take one of your old ones and weigh them; I would be very surprised if your new wheels aren't significantly heavier. Given that, my rule of thumb has been ~$300 per wheel or more to get lighter than factory as cheaper ones tend to be more or less the same weight as factory accessory wheels.
In reference to the ECO mode and the wheels, I would consider that they sell and test the factory boat anchors (although they have gotten lighter than they used to be) and the milage drop isn't enough for EX and EX-L people to complain but notice that the hybrid and the HX have different factory rims and wheel covers which suggests that under those circumstances -i.e. fuel economy being of primordial importance and owners who will complain if milage drops by 1mpg- they do not sell the factory boat anchors for these models and I wonder if they would be willing to install them without some sort of paper that says "we told you so". Based on the difference in MPG between EX and LX, I would say that there is a 4-6 mpg difference between factory rims with wheel covers and factory boat anchors.
One last point: some aftermarket rims that look great (some might even be light as well for all I know) are aerodynamic disasters. That is to say that at 25-35 mph they are fine but at 80 mph they are like wearing a parachute.
