No, natural gas vehicles are not a good idea. It is my opinion that to develop natural gas vehicles to the point that they would be consistently road-worthy would cost far too much money. This is especially true when one considers that other alternative-fuel vehicles are being developed for much cheaper.
Using natural gas to power vehicles only shifts the burden from one resource to another, not solving any of our economic and environmental issues. We need a renewable, clean resource, like solar power, to use as fuel for our vehicles if we wish to continue driving them in the next 100 years.