Generally, I think we as car model builders do tend to weather too evenly. That said I partially blame rat rods especially the ones who put false patina on their cars. If you check out people like Dr Cranky, Chuck Doane, Bill Borgen and Dave Roehrle, they have weathering down quite well. Also if you have a chance check out the Weathering Civilian vehicles book by A.K. Interactive. Great work there.