I have color dmd's in Tales Of The Arabian Nights, Judge Dredd and I just picked one up for my Tron (but haven't installed yet). TOTAN is phenomenal with cdmd, it really makes that game shine and fits with it perfectly. Gov did a great job coloring the dots on Judge Dredd, and as a fan of the original comics, the palette he chose is spot on. Tron, from the videos I've seen (having not installed yet), looks good, but isn't nearly as necessary, though it will be a fun game to play around with different display modes. I think the nice thing about cdmd is that it really helps bring a clarity to the existing dots by giving some contrast, which makes it easier to quickly look at the display and still get all the info. Besides that, they look better and they certainly make the games more attractive and modern looking. I agree with pingod, GOT will really benefit from a cdmd, as it is showing a lot of detailed stuff that could use some more contrast to make it pop.
Is it worth the money? No, but I still will buy one for every game I own because they make the game look better and pinball is visual entertainment. That and you can always keep it and swap in the factory display if you decide to sell.