Theoretically speaking (keep in mind, however, that I DO have a spiraled TB spacer!), the smoother the whole intake part, the better the flow of air. Laminar flow (which is what you get when air flows without turbulance) allows for the fastest flow of air, so a spiral would actually slow the air down, reducing the amount of air the engine can breath, and thus energy...
Having said that, the reason I do run a spiraled TB is that the above is true for WOT. But in partially opened throttle, the spirel could possibly help to improve the flow (in my opinion, anyway). I have yet to do tests to prove this, but I have heard from some people that you get more power from the 4.0TB without a TB spacer than with...
Felipe