The Jeeps and Chevettes that I saw or bought all had plastic bases. To my knowledge, all of the Fresh Cherries have metal bases. I can't remember about the Impalas and Caprices in AG. I'd be willing to guess they were plastic as well.
Hmmmm? Well I have a question in to the powers that be to see if metal can be done. I know we all prefer metal. If you notice, it looks like they have a formula of sorts for different qualities. The standard 3" car as they call it has a plstic base and one piece hard plastic wheel. The AG has the upgraded multi-piece rubber tire and rim but a plastic base along with upgraded graphics. The Fresh Cherries has the metal base, authentic detail and there is crossover in all segments. The Vega is in FC and in AG. Most of the AG are also in the 3" line so perhaps they are all mix and match? If so it opens up many more possiblilities.
Check out the 3" stuff. if you can invision upgraded FC style wheels on many of those castings, they could look very nice. I for one would like to see the VW show car with a metal base and rubber wheels. I bet that casting would look great.