Give her the G35, keep the 4Runner for yourself.
The G35 over long distances is liable to get you into more trouble (speeding tickets) and with the amount you drive, you're more likely to be in an accident in which the 4Runner will help you out with.
The gas mileage is a pretty moot point, as if you took the G35 and drove far (and probably fast) the mileage would come down.
Because the G35 is using the VQ engine, it'll last longer than the car itself (notice any creaks? squeals? how is the transmission? how is the wear on the tires?), but the car won't last as long as the Toyota.
Because you're spending more time in the 4Runner, the additional space is nice to have for "things" (spare clothes, gear, etc.).
BTW, you didn't mention "Coupe" or "Sedan".
2006 G35 (6MT Coupe 60k+ miles, iPod, Nav, RAS, etc.)
2008 4Runner (40k+ miles)
My sister drives a 2005 G35 Sedan. If it's a G35 Sedan, yeah, that's definately a chick car.