I too have the Canon 30D body, but with a Tamron 17-50 f/2.8. It's a pretty good indoor lens, but it's certainly no prime. The wide angle aspect is great especially when trying to get a shot of all of the family...but I really need to get a hot shoe flash.
I rented a 100-400mm L lens for this week and I think it takes sharper images than my Tamron does...it also retails at ~$1700 It works very well as a zoom lens on these crop bodies. Because it's an EF lens, the built in 1.6x multiplier effectively makes it a 160-640mm.
For your night shots, I second the request for stopping down your lens. Give yourself some nice long 5sec or longer shutters and watch those car lights blur.
For your colors, go into your menu and check your settings. I notice a difference when I select portorait (sp), landscape, neutral, ect... You can also adjust your hue too. I don't know where you can adjust your dynamic range though. I think it's all sensor dependent.
As for the 40D, it is a little better than the 30D, but I wouldn't go for the 50D. It uses the same sensor as the 50D but because they force 15MP out of it instead of 10MP, the image quality is actually degraded.
http://www.dpreview.com/reviews/canoneos50d/
Modified by Looneybomber at 6:30 PM 8/2/2009