I ran across this and thought this might be a good article for you to read.
Myth #4 It's pointless to add more pixels because lenses aren't good enough.
Reality: I have no idea where this one came from, because it's contradicted by decades of lens and camera test data. I'm going to cut through the morass of minutia-based arguments about pixel dimensions, filter geometries, and Airy disks and lay it out in very simple terms. A 16-megapixel 35mm-sized Bayer array sensor is going to resolve around 50 line pairs per millimeter (lp/mm). A 36-megapixel sensor will resolve around 75 lp/mm. Even mediocre 35mm lenses will hit 75 lp/mm at some aperture over some portion of their field of view. This is true of both fixed focal length and zoom lenses. Decent (not at all exceptional) 35mm-format lenses can hit 75 lp/mm at just about all apertures and will do so over most of the field of view for at least one aperture. They'll show peak resolutions more like twice that. Really good lenses (not necessarily expensive ones) will be able to exceed 75 line pair per millimeter without even trying hard over most/all of the field of view and will have peak resolutions three or more times that.
Furthermore, until the lens resolution drops to only half that of the sensor, improving sensor resolution will produce an observable improvement in image resolution. See the previously cited diffraction column and "Why 80 Megapixels Just Won't Be Enough..." - And if you would like to read all of it, here is the link: