Based on history, the way NASA tends to improve missions via software rather than hardware. For example, stitching lower resolution images together rather than developing a higher pixel count camera.
Getting a camera there is far more important than its spec sheet, and given that the lifetime of nuclear powered instruments can exceed 30 years (e.g. Pioneer and Voyeger) any over-achieving mission is going to be dependent on obsolescent hardware for a very long time. When Curiosity was developed, the choice of a four megapixel camera would still be quaint by today's consumer expectations.
Getting a camera there is far more important than its spec sheet, and given that the lifetime of nuclear powered instruments can exceed 30 years (e.g. Pioneer and Voyeger) any over-achieving mission is going to be dependent on obsolescent hardware for a very long time. When Curiosity was developed, the choice of a four megapixel camera would still be quaint by today's consumer expectations.