Just to add my 2 cents, I've seen about half of the new Bullitt DVD. Without doing a direct A-B comparison, I can tell a difference alright between this disc and the first Warner DVD.
I have the VHS Warner tape, the Warner laserdisc of the film that is fullscreen (wow, $24.95 for 1989), the first Warner DVD and now this new SE of Bullitt. In each edition, from memory, there has been an incremental improvement in the video, with this edition being the best and most improvement. I agree with Crawdaddy's comments above on the video quality, this new edition is darker and denser. And the audio commentary from director Yates expalins why it's so dark. I do recall some nice stereo effects on the VHS and the laser has nice bass too.
The one thing you'll find amusing is that on the fullscreen laserdisc, you can just catch the top edge of the boom mike on the bottom of the frame. Perhaps this is common knowledge, like the number of times you see the same Volkswagon during the chase sequence. The sequence to which I refer is when the killer is at the hospital and is asking a doctor where to find his "relative", at 37:35 into the film.