It depends on what you want to use the images for. For the internet, 1mpx is clean and beautiful, and for newspaper or magazine publication, 3mpx is enough. I printed a 30x90cm photobook and they reached 12 mpx.

It also depends on what your subject is & what lens you have available. For small birds I'd generally need more than I have (along with better focusing/sharper optics).

If I don't have to crop the hell out of a shot 16MP has always proved more than plenty & I rarely had problems when I only had 6MP.

What the elapsed time has taught me: "There is no such a thing as enough Pixels"... and in due time, as our technology improves, we get more of Pixels, all the time and sometimes, and to surprise more, "More is for less". That is you get more Pixel for the less price tag you pay for the better technology. So don't settle for a number and enjoy "What comes May", that is really better when less is what you pay!