The other argument I always make:
You're buying two 2002 Mustangs. One is a v6, one is a v8, otherwise every single thing is identical about the two. For the cost difference, you can make the v6 reliably blow the doors of the gt if you know where to spend your money.
Most people just waste their time with exhaust and bolt ons.
This.
The BIGGEST problem I see is that people get SOOOO hung up on the "I will never own a V6" blah blah blah..... They don't really know anything about the motors. People who like to say "I had one and I modded it, but it still sucked..." When you start to talk, they wasted money on mods that don't do anything b/c they did something on a GT. They aren't the same motor. People that educate themselves before passing judgement are the 'niche' of V6 owners who have/will/will continue to be able to show tail lights to the GT counter parts for the same budget.
Believe me, I started buying Mustangs in the mid 90's. I was DIE HARD fox body guy. I had several V8s and I still have V8s. I got a V6 (Roush) as an impulse buy. I still had my 347 powered fox when I bought it and when I sold it I also had my SC'd V8 Roush. I started taking so much heat about the V6 I decided to see what it could do. Did I start just slapping on a CAI and bolt on junk? No. I started with research. Where are the bottle necks in air flow? Where can I make improvements? What is there for aftermarket? What are other owners/racers doing to make REAL power? Quite frankly, in the early 2000's (when I started into it), there wasn't much info out there. That is why I started building my own parts. Can everyone do that? Not a chance. But with the expansion of forums, and years spent working on the good old pushrod 3.8L cars, it's very possible to take a limited budget and make more power than a GT with the same money spent. People who say "Sure you can make anything fast with enough money", it doesn't take a lot. Like was posted, you can make the same year V6 on par or faster than the GT with the price difference if you know what you are doing.
Then it comes down to personal opinion: Sound and spark plug count.
I loved the sound of my side exit on a stroked/boosted V6. I never had anyone tell me they didn't like it. Again, too many people slap on exhaust they think should sound good b/c it works on a V8. They aren't set up the same, so you need to shape the sound differently.
Spark plug count is something I laugh at. I hear it all the time "I'd rather drive a good sounding V8 that's slower than a V6". Fine. That's your choice. If I have to pick one, I pick the faster car for less money. End of story.