If I just had my throttle body and intake manifold bored out, could I get relatively the same effect as aftermarket products? Would this be worth doing? If so how big could I/ should I go? Is a new butterfly valve all I would need?

Holla.

 

just get an integra TB, ls will pretty much bolt-on, GSR is a bit bigger, but needs a new throttle cable bracket. then if you want to keep the stock IM, look into Extrude Honing. you will probably have to send it off, depending on where you live. but the best power would probably be an Extrude Honed aftermarket one.