I also started getting serious about photography in 1961, and recently acquired a new D800E in January. Since then it has become my most used camera. My D3 is working fine, and I still use it when speed is more important than resolution or DR.
I waited, not due to any concerns about camera problems, motion blur or diffraction, but simply because I did not feel a compelling need for an upgrade. My main motivation in getting a D800 was for higher resolution in macro and close up work. However, I have used the camera more often for photographing our grandson, and have sometimes taken advantage of its DR and extra megapixels for cropping, to get shots I would not have managed otherwise.