More "reach" with the same lens is "achieved" with a smaller sensor (DX), which is simply a crop, but it has to be enlarged more, which is a telephoto effect ("reach"). You can easily see this in your editor, just zoom any image larger, which shows as a crop, which is enlarged more. Same visual effect as zooming with a telephoto lens (except lens zoom could show more detail, and we have fewer pixels if cropped after exposure).
More lens resolution shows more image detail. Digital sampling resolution (pixels) simply tries to reproduce that detail, more is better. More pixels is not "size" or "reach", and sampling cannot add detail to the original lens image, but more pixels will reproduce it better, with benefit to greater enlargement or cropping. Enlargement is what gives "reach" (done with longer lens, or via crop and enlargement).
Megapixels is sampling resolution of the lens image. Nyquist rule says 2x sampling is MINIMUM requirement. More is better. Those suggesting otherwise probably never saw it, and DxO sort of has their own numbering ideas.
Few of us have the necessary cameras to compare, but probably we have a scanner (which does the same digital sampling as the camera does, same concept, and can easily show us).
Scan a photo in a glossy magazine, printed halftone which is likely 150 dots per inch.
If scanned at 150 dpi or less (1x sampling or less), we get moire, which is aliasing, false detail due insufficient sampling, less than Nyquist 2x minimum.
Scan at 300 dpi (Nyquist 2x Minimum), and it looks better, with no moire. Zoom it to 100% size and examine detail of the halftone dots... dot reproduction is vastly better than at 150 dpi.
Scan at 600 dpi, and zoom it to 100% size and examine detail of the halftone dots... better yet than at 300 dpi.
Scan at 1200 dpi, and zoom it to 100% size and examine detail of the halftone dots... better dots than at 600 dpi. More is better. Starts looking fair at 8x sampling.
Previous scans look OK at "normal" size, but 100% of the detail shows that 8x sampling is better, and more might be better yet.
In this case, the goal of sampling is to reproduce those dots, which is the only detail that exists in this image.... 150 dots per inch.
If our photo image has lens detail at 100 line pair per mm, then just 8x sampling is 800 pixels per mm. Our current FX/DX cameras only do more like 200 pixels per mm (barely 2x, except little of our data is at 100 lp/mm). We are not yet near any limits. Our goals for using the image may be a limit for this instance (we can only print so big), but is not a technical limit.
Newbies imagine 1x sampling suffices, but far from it, it is not even Minimum. Digital sampling is a new concept for many.
Digital resolution - more is better. Up to a point (well past 2x sampling), because the best result possible is merely a reproduction of the lens image. Digital sampling cannot add new detail that the lens did not see.
This is 36 megapixels, Nikon D800 camera, which is available, and pretty nice.
(click to enlarge)