Definitely following to see side-by-side comparisons in-game. Ideally, one half of the game would be original and the other half with Black Diamond. That way we could see not only the difference on the vertical surfaces, but also on the curved and sloped ramps.
I play in a darkened basement, so this isn't a HUGE need for me, but the projector is so central to the mood and visuals, that I would be in if it was a significant upgrade across all the target surfaces.