there is actually alot of hp to be picked up by changing tired old valve springs for a set that properly match's the cam. If i were you i would swap new ones in. You can change them on the car there are tools to do that. Then you wouldn't have to remove your heads. Its not that new springs are going to give you more hp its that they will bring the engine back to where it was before they wore out. You may also find you can rev it higher because you are not experiencing valve float.