On the surface, it might look good, but if you think about it, it could decrease performance. A straight path offers the best flow. When you spin the air in a vortex, it seems that it would create a condition whereby the fuel wouldn't mix as efficiently as the straight flow, and it seems that it would make the air meander, rather than shoot, though the engine. The proof is that no manafacturer is using such design. You cannot have a patent on the way air flows, so all you would have to do is make your own design that would duplicate the vortex flow.

As far as people swearing by modifications, I have seen people install loud mufflers that actually decrease engine performance, yet they swear that the modification makes the vehile into a rocket.