none of these things actually ADD power.

a TB spacer changes the dynamics and length of the intake. that means a lot, or a little. you would have to calculate the gains vs drawbacks. however i feel that a half inch spacer doesnt do much. if you go into the 2 inch lengths, then yes. it will change.

pullies are a misnomer. most of the time they just gear things down because at higher rpms, things like to fail sooner such as water pump, oil pump or alternator.