What "is" and "is not" worth it to add performance upgrades to your V6. Most of the negative input about upgrades comes from GT owners (God's gift to the Mustang world).
If you're a V6 owner and you want to improve your performance I have found that adding headers and any type of dual exhaust has its benefits. Your V6 breaths better.
In reality these upgrades add about 10-12 hp to the rear wheels. Add an underdrive pully maybe another 5-7 hp. Forget the manufacturer's hype. Are these upgrades worth it? It depends on your personal goals for the performance of your V6. Will it perform better? Yes. Will it sound better? Yes. Will it beat up on a stock GT? No.
Another reality is that you've spent about $1000 for less than a 10 percent hp gain. BUT...if you build from there (ported intakes and a 65mm
BBK TB) you've now doubled your gains to 20-24 hp to the rear wheels for about another $1000. Add stage 2+ heads a roller cam-roller lifters-roller rockers-hardened push rods and you've added 100 hp...So for about another $4000 you have 270hp to the wheels. Add forged pistons and a 30 over bore...310hp, and you're ready for a power adder (turbo-sc-nos) and you'll double that to 650hp...you blow out your 7.5 rearend add a 8.8 $1100.00...subframe and
control arms $600.00 ...seeing a GT disappear in your rear view they're looking at your 3.8 badge...priceless.
If a GT adds the same upgrades...