Alot of the performance mods on the market are gimmics. Take the TB spacer for an example. The theory behind a spacer on the TB is tune the harmonic reasonance of the intake system so that a positive pressure pulse hits the back of the intake valve just as it is closing to force jsut a bit more air into the cylinders. You ever look at the engine on an indycar? notice how the intact manifold looks like a wierd maze with stuff jutting out the top? That is a good example of near perfect intake tuning. Another good example of intake tuning is edlebroke intake manifolds for big V-8's. If you change the arc the air takes or the length of the runner or the chamber volume you can make them work really well through certain RPM's. TB spacers don't work for 2 reasons; 1, they don't change the volume or the runner length by a significant amount, 2, they are in the wrong place to change the harmonics. Because they are at pretty much a 90 degree angle to the pressure pulses coming off the intake, they have little or no effect. Instead of the pressure pulse bouncing off the back side of the TB, they bounce off the opposite side of the intake manifold.
Most of the bolt on cheap mods are like this. Unless you fork out the cash for a mod the really works (IE Header, new ported head, camshaft, etc...) you end up changine the sound of the engine without making any significant power. Run us buy a budget and ideas you have, there is a reason why it costs alot of money for an engine that makes lots of power.....
