SD headers will do about the same as a plog and downpipe.

SD headers are $200ish

Plog (no longer on ZZP site?) were ~$200
Downpipe was at least another $90

Maybe they don't add much, headers don't take anything away either. Sure you may lose a little low end, you'll still be able to beat the trans and smoke tires from a stop. I say..what are you losing, spinning is spinning and that's not winning.

A downpipe only helps a bit with the u bend restriction. Ask your neighbor about the front manifold restriction. IMO it's the biggest restriction on the motor, exhaust wise.