The new PSR-S670 has omitted the screen buttons entirely, and relies completely on the data wheel and enter button for scrolling through and selecting screen items. I wonder if this could be a harbringer of things to come for the rest of the PSR-S line. In view of Gary's comments on the carbon contact switches, this would be ten fewer items to go bad.
I doubt it very much. The 670 is a different beastie to the 9xx models. A lot closer than the previous 6xx models, for sure, but not the same. The O/S of the 9xx is more advanced, and I personally find the scroll, dial, press enter etc method a PITA! If we see a big change to the 9xx models, it will be a move to a touch screen, I'm sure.
Carbon contacts are here to stay, they're found in just about everything and have been a bit of a pain since they first came on the scene. It only takes a bit of grit or dirt to get in and the problems start. Unfortunately many people then start pressing the button harder and harder to try to 'fix' the problem. Alas, this just makes it worse. The only real solution is to open to keyboard up enough to get access to the offending carbon contact, then either use an air can or, better still, some denatured alcohol on a cotton bud/Q-tip. While the contact is exposed, you may as well do all the others. Sometimes you just have to replace the contact strip.
None of the cleaning or replacement processes take much time in themselves. Dismantling and reassembling the keyboard - that's a longer job. Just be thankful you don't have a top of the range organ to dismantle - they can take hours!