I had the same phone as you, the 16gb black, up until recently. I played with the new one in the AT&T store on launch day, and I knew I had to get the 3GS. It's just so much faster and responsive. That's the main reason to upgrade.
I also wanted the video camera, but the main reason was just being wowed by how fast it was in the store. I touched the ipod icon, and bam the song list was right there immediately, like not even a 1 second delay (of course in hindsight, I realize that the model in the store probably had a small itunes library, but still). Also the SMS app loads very quickly too. Maybe 1 or 2 seconds to load it, instead of the sitting there for 5 or 6 seconds on the 3G.
So I was even willing to pay the early upgrade price of $499 to get it after that experience. Go try it in the store and see if it's worth it to you.