My car has the HSR intake set-up with a BBK TB.

Is a throttle body spacer a decent upgrade worth doing?

Should i buy a holley 58MM TB to replace my 52 MM BBK?

Theres also a flow booster out there... are those worth buying/ installing?

 

If you are using a stock cam and/or stock heads the extra flow of a 58mm TB will not be advantageous - Your engine cannot use it. Consider the fact that the 502 RamJet used the same stock 48mm TB on the 500+ CID engine to make an honest 500+HP, and you may realize that intake flow is probably not the most significant factor limiting power production. You already have a 52MM TB and probably aren't pushing out 500HP (yet).