I didn't vote, as I'm hardly shooting these days, but slclick's comment inspired me to write my own journey.

I went from 15.1 MP (T1i), to 18 MP (7D), to 16.6 MP (1Ds mk II), to 20.2 MP (7D mk II).

T1i MPs weren't the issue, it just couldn't AIServo fast enough to track a running dog. After getting the 7D I noticed images were now sharper, but I hadn't really noticed while using the T1i. More MP wouldn't help when it's already not using the existing pixels well.

7D was fine. I occasionally felt I could use more MP for cropping. Biggest problem was the burst rate exactly matched my dogs stride time, so I'd get a series of nearly identical dog pose with changing backgrounds.

1Ds mk II was great. Pixels were sharper than 7D, pictures had a great feel to them. Had great highlight handling the 7Ds couldn't touch. Controls and menus are a mess though. You couldn't exceed ISO 1600 though... that sensor really didn't like low light.

7D mk II felt like a mistake. Visible noise in well lit ISO 100 images, but only minor high-ISO improvements (in camera JPGs looked much improved, giving an early impression of much better high-ISO handling until ACR added 7D mk II support). Auto-ISO M mode finally getting exposure compensation was great though.

Judging by my feelings towards the 7D, 7D II, and 1DS mk II, I don't primarily want more MP. I want cleaner images with nicer tone and excellent highlight handling above megapixels... but I also want up to date controls, and decent AI Servo performance. Unfortunately, that's a combo that means investing more money than I'm willing to at this point.

Note, that while I did feel I could use more MP on the 7D for cropping, the increased noise on the 7D mk II to get just a fraction of the MP needed to be useful meant I no longer craved extra MP on a crop-body. If any FF high-MP body experienced the same gains in noise as the 7D2 did, I'd also consider it a mistake... for me. I'm sure someone would find it useful, but high MP is not the only goal, and likely not the goal of most.