Well, I upgraded my TB for 2 reasons, first, it seemed like there was play in the throttle shaft(throttle open it would wiggle slightly.) Also, because the up pipe is 2 1/2 inch or so ID, and the stock TB is like 2 1/4 inch ID, minus the throttle blade, etc. It seemed to me that the smoother flow/less ID change would be a good thing. It seemed to have better throttle feel too, afterwards. IMO I think it's worth it,,, I think Jays' is like 95$, although I have a 65mmm not his.
As an aside, I also shortened the screws that hold the throttle blade in place so the don't stick out the back of the shaft,, prolly worth 20 hp,, and I sharpened the leading edge of the throttle blade(careful here, don't want to sharpen the wrong side and affect idle.) The 65mm TB has a thicker Throttle blade than stock.