Thanks for well-thought comparison, it's good to hear from people who use both.
I don't imagine the contrast on any eink device will be adjustable, the only way to do that would be to use the grey levels available to fake it.
What kills the LCD devices for me is size and battery life - you can only have one at a time, and often not much of either. 2 hours is a joke, even 12 hours is not very useful unless it can plug into mains power with a very small, portable adapter. And the 505 is limited in screen size from my point of view - I'd rather shrink the bottom buttons in favour of another 30-40mm of screen. So while I'd appreciate more contrast on the 505, I wouldn't trade it for any of the LCD devices I've yet seen.