So far no one has addressed: "Will headers make enough new horsepower to merit dropping $800 or whatever they cost to the exhaust I currently have?"
Frankly, you will get a large amount of opinions on this. For a stock or mild build, you wont get any kind of seat of the pants feel. I beleive headers really dont cone into play unless you have combo of things together that make them worth it, like a good set of flowing heads, a good cam/carb combo, etc. And even then, mid to high range rpms is probably where they come into play
Bottom line a basically stocker or mild engine, to me with a 2 - 1/4 exh, is not worth the 800 price. Add another 150 or so in labor to that if a mech does the installation