As above I think much depends on what final outcome is wanted. 
Certainly number of pixels is not the only consideration because a limit will be reached where the sensor is out resolving the lens and requires higher quality optics to produce a finer image.  At the point where budget for the camera matches expectations of outcome is the happy position most of us would like to be able to achieve.  It is not easy, and things get muddied by the whole marketing hype so rational decision making is almost impossible. Throw in that for most people a camera is a personal item and pride of ownership etc plays an enormous role in what people will want, technical specfication to perform the task sometimes becomes only one of the prime movers in decision making. 

And every one said, 'If we only live,
We too will go to sea in a Sieve,---
To the hills of the Chankly Bore!'
Far and few, far and few, Are the lands where the Jumblies live;
Their heads are green, and their hands are blue, And they went to sea in a Sieve.

Edward Lear
http://www.nonsenselit.org/Lear/ns/jumblies.html