Is Yosemite (at least the parts you can get to in winter) that snowbound? I lived on the wrong side of the Sierras (Tahoe on the NV side) for a few years and never noticed snow to be a problem until you were at or above 4-5,000' ASL on my rare winter deep forays into California. I guess there's that wicked climb at Groveland. Maybe make a 4WD rental as well as one for a normal car, and just take the car if the weather forecast is for sunny skies.