Everyone is missing the point here. The problem isn't that these cameras are old tech and using outdated CCD censors. If these were the best images we've seen to date of Mars, you're right, there'd be a "Good Enough Factor" — the best images we've seen from a NASA mission, but not as good as modern DSLRs. Understandable.
You are comparing the very first initial images from Curiosity with the final processed images from Viking. Also, the haz-cams on Curiosity are there only to help Curiosity see where it is going. Whatever design trade-offs they make, they need to make the priority be "don't break the 2.5 billion dollar rover that is supposed to last for over a decade."
If you use a low-res camera to take 1000 images of the same thing, you can use software to make a high-res image from those.
The problem, that I think a lot of people are missing, is that Viking 1, from 1976, took higher quality pictures of Mars. http://f.cl.ly/items/0k2w2d1C1O3w3e0t300f/NASAQualityDegreda...