I thought I might share this idea. I have no way to know if it will actually help as it will take some time for the button to crack or not. However, I looked at what is happening on my two nooks when I press the button. They both are current WiFi only models but one has a significantly softer touch and a different face plate for the touch screen. I determined that the softer model is moving less when the button is pushed and that the button is much quieter which leads me to believe that possibly they made some changes to try and fix the breakage problem.

Given that there are only two ways to deal with this, improve the material or decrease the flex that is causing the cracking, I figured if I could add something in the space between the bezel and the button, I could decrease the travel and extend the life of the plastic. So I took off the back, got some thin flexible plastic, mine came from a piece of clear throw-away check book cover, and I trimmed four small rectangles with a tab, which would slide between the bezel and the button. The tab is so I can remove it as the rectangle was cut to fit completely out of sight. It fits perfectly and inserted with no trouble. The tabs fold over under the cover and the whole thing is out of sight.

The good news is that there is now less travel when I push the buttons so I should have less stress. Only time will tell.