Dear Mick.
My CCD uses a parallel port so I am not the best to give an opinion but I don't see what difference it would make. Even with my camera downloads are about 15 secs for the highest resolution. Subframes are much faster. When you are doing 3-5 min exposures waiting 15 secs at the end is not important.
I assume the advantage with firewire would be speed but even with webcams doing video exposures rather than stills I can't see a time when you need more than about 1/30 sec exposures. This is perfectly good for focussing or planetary imaging. There would be little advantage going faster as this speed will "freeze the seeing". Most of the objects we image are not that bright to need faster.
The reality is that the firewire port is faster and it has a consistent standard for what fire wire represents. USB has many standards and this may not be a wise move for the imaging source. I had the fire wire version but replaced it with the lumenera skynyx. One observation I have made so far is the skynyx can hesitate more often than the DMK ever did. This is at the same frame rates and same 8 bit density. The skynyx uses a USB2 architecture.
USB is good, but if plugging in a few more wires means removing the hesitations then I will go with that. The only real advantage I have seen with the new camera is the low noise and greater well depth. If the imaging source had offered these then I would have stayed with them. Alas they did not.