I just interviewed the product manager at Sony for Vegas 7 (for a magazine article I'm writing), and he said they love Cineform and recommend it for use with Vegas. For what it's worth...
From what I understand, and from the examples I've seen (follow the link I included above), working in the deeper color spaces allows for a smoother and more precise manipulations of your image.
In the article in the link above there are color pictures where you can clearly see the difference in interpretation from the different actions in the different color spaces.
True, you're going to distribute in SD, but the crushing of the colors is occouring by the use of specific tools in specific color spaces. Just as we've all learned that shooting in HD gives you a better picture in SD, working in 16 or 32 bits per color channel will give us a better manipulated picture in 8-bits per channel.
