The resolution of a camera system is, as you probably know, a product of lens and camera. A lens will thus never "outresolve" the resolution of the sensor, nor vice versa. More megapixels will, ceteris paribus, give greater resolution, as will a better resolving lens no matter the resolution of the sensor. (If more resolution is your goal you should, hovewer, update the "weakest link" first since, arithmetically, increasing the lowest of the two factors will yield a the greater product).
When it comes to motion blur, a photography printed the same size will not be more blurry with a higher resolving sensor (or lens!). The potential resolution of the sensor will, of course, only be achieved with adequate stabilisation/high shutter speeds.
I'm not a sharpness fetishist, by any means, but especially appreiciate the fact that high resolving sensor can bring old, somewhat soft—but otherwise beautifull—back to life, so to speak, by giving the system as a whole a little bump in resolution.
PS: I'm sure we are in agreement on these points, I just wanted to clearify for the sake of readers not wrongly getting the impression that more megapixels will give more blur with same print size (or the related misunderstanding that the additional megapixels are totally lost on lower resolving lenses).
