Newbie here, I have an '02 rwd Blazer 2dr LS with the HO 4.3L Vortec.
I'm aiming for more power, the same if not better fuel economy, and that low v8-like rumble. I plan to install a cold air intake, high-flow cat and muffler, 2-1/2" exhaust pipes, mod the MAF, and have it tuned for the new flow once all done. May upgrade the camshaft later down the road.
Would it be worth it to put headers on when I redo the exhaust? Or are they just a PITA that's best avoided unless you plan to be turbo/supercharged and pushing +350hp?

 

Headers alone, or even combined with a full exhaust upgrade won't make a huge difference. My brother's S10 mini is significantly lighter than my Sonoma crew cab, and his has a fully upgraded exhaust including headers and high flow cat, and there is no noticeable difference driving the two trucks.

If you do all the upgrades you've suggested like full exhaust, intake, fuel system, upgraded cam, AND a full tune from a professional tuner to take advantage of the changes you've made. then you'll probably see some decent improvements. It might even get you up to the same level as if you swapped in a bone-stock 5.3 LS.

It's too bad there aren't any of the supercharger kits for the 4.3 around anymore. Those really could wake up an S10.