Bias alert: when I was younger, I loved headers. As I've gotten older and more experienced, I've taken them off everything I own and will never put any back on, unless they're the rare factory Ford cast iron headers. I do have a 406 with those on it.
Headers help the evacuation of spent combustion gasses from the cylinder. They also reduce the backpulses from the cylinder into the intake manifold as the intake valve opens, resulting in a more even flow (but still not entirely smooth, by any means) of fresh air and fuel vapor into the cylinder. Think of the combination effect as a bit extra air and fuel entering the cylinder, like free supercharging.
However, this effect is minimal at low to moderate loads and RPMs of under 5000. Where you see the greatest positive effect from headers is under heavy load at higher RPMs, the tube lengths and overall design affecting where in the RPM range the effect is greatest. This could be flat-out racing or extended hill climbing with a heavy load. If you are not engaged in either of those two, you're going to find headers to be a way more expensive and headache proposition than any possible benefit you'll get from them.
The FE engines in our trucks almost all face ordinary driving conditions under low to moderate load and engine speeds. Header benefits under such conditions include:
1) increase of ordinary torque of about 10-20 ft-lbs under 3500 RPM
2) horsepower increase of about 5-10 under 3500 RPM
3) fuel economy increase of about 1/2 to 2/3 MPG
Header drawbacks under such conditions include:
1) Cost of headers, decent ones in excess of $300 plus high quality gaskets
2) Ceramic or other temperature control coating to extend life in order to reduce heat radiating to starter $200
3) Installation of headers, including new exhaust system to fully take advantage of them, about $800
4) Recommend smaller starter to accommodate heat shielding, about $300
5) Occasional/frequent gasket failure, requiring reinstall
6) Heat soaked starter problems, occasional outright failure requiring starter replacement, troublesome with headers in the way
7) In-cab noise increase of headers is often noticeable, to some ears highly annoying
Cost of headers done right, approximately $1,600
What you get for $1,600 is mostly noise, ongoing maintenance issues and bragging rights, the glow that comes from having performance parts that other people think are impressive, but really aren't for daily driving. What you don't get is much improvement in performance or fuel economy under ordinary use conditions.
If you're pulling heavy loads at higher RPM's, or if you're racing your truck, then there is a much better case to be made for steel tube headers. Or if you just "want to".
Here's some additional good information to soak up on headers if you're truly interested in the subject
http://www.hotrod.com/articles/header-basics/
Hope this helps.
Now the decision needs to be made. Buy another set of fancy pipes, or back to original equipment? 
