I also fly around 70-80 sectors a year and was last upgraded about 3 years ago on a US Airways transatlantic flight. Occasionally fly business, but normally fly on the cheapest tickets and with different airlines so only have silver status with KLM.
To be honest, I don't really care which airline I fly with or what class, and certainly wouldn't pay for business out of my own pocket. A lie flat bed can be nice, but I never sleep anyway, don't really want to eat onboard and can't be bothered with the inflight entertainment.
I do appreciate easy transfers and quick boarding which I get with my KLM silver card anyway.