So, let's go one after another:
1. 90% of the GT5 post are about tracks and cars wishlists, working reverse-lights manifestos, arguments is Forza better then GT and so on. So, 90% of the post are here just because there is many people on the world who like to share their ideas about their favorite / hatred game series.
2. If you think it's the waste of your time, then why are you here? If you think PD will come here, read some of ideas and then implement it into next GT game, then you're wrong. Thay had 99% of those "new ideas" probably somewhere around 1999, and remaining 1% around 2001. Right now in late 2007, they're recosidering ideas we'll come to in 2011 respectfuly.
3. PD KNOWS that their sound isn't good. They know it better then we do. Why? Because they have an actual chance to listen all those cars EVERY DAY in their life. And they probably have a very good reason why they've sacrifised the sound in order to achieve someting else somewhere else. It's called "smart usage of limited resources".
4. We all come here to have fun and share some thoughts. Nobody ever think we can make a true impact. Why? Because we know PD is doing their job the best they can to make GT series be THE BEST racer around. Everything else is just wishful thinking.
Have fun man.