It may be more cost effective, but in my opinion, it's not proper. When I see a tube frame race car in GA, I feel as if the manufacturer's saying, "We don't have anything in out lineup that can even remotely compete with what they have, so we'll just jump in NASCAR style and put one of our car's body panels on a tube frame and no will notice". In other words, it's a poor excuse for a race car. I believe if manufactures want to compete, they have to use one of their real cars and tune it up. Now I know in sires like the ALMS GTE category, most GT cars are no where near stock, but most of the underlying bits are either direct from the factory, or swapped over from the actual street version. They are therefore the pinnacle of what that road car can be, and the manufacture stands behind them. But with tube frames, you get almost no factory/street components, and much less factory support.