wheel discussion for mpg

[tire]

i come from the mustang world and this import business is pretty weird to me. i have an 07 yaris (base) sedan and got 37.3 mpg with 30% street / 70% highway on the 4-spd auto. (i feel i must vent how much i dislike autos... i'm trying to be a responsible future-family man)

i did a search but came up wanting. i'm interested in finding a similar sized alloy/otherwise lightweight wheel as my stock steel 14 inchers so as to improve mpg/kpl and not cause any rubbing issues.

basically, i'm attempting to find non-invasive ways to improve the car. non-invasive meaning nothing permanent or at all risky. this is obviously my daily driver and could potentially be resold, so indications of modification are not wanted. lightening the curb weight is another possibility but i'm not sure where to start, so i figured a lighter wheel would be ideal for bang-for-the-buck-ness as it covers both rotating mass and curb weight.

austin

PS - i'm a tard for not putting this in the wheel/tire forum, my apologies.