I posted a short article on my website about de-interlacing with Vegas. I included full-rez sample stills from a narrative short film that originated in 60i on my JVC GY-DV500 and then de-interlaced to 30p.
I can't see the difference in the static shots. The panned shots look like the double images you get from the "render lower field first and combine method. I like DVFilmaker de-interlacing better personally.
If you're really serious about it send it to a post house with a pro box that does de-interlacing using motion compensation.
The 500 is a great camera but I think you'd do better with the DVX 100 if you want the progressive look. Pretty much the same level of control as the 500 if not more. Can't really comment about the optics, would also depend what lens you put on the 500. As you're shooting 16:9 have you thought about the 700? Don't know if JVC still have them in production or not.
Bob, you're absolutely right that the ideal solution is to aquire in progressive. This is my stop-gap measure until I can get my hands on either an XL-2 or a decent 1/2" or 2/3" 3-chip HDV camera.