It helps to be good, and it's even better to be lucky and good; they were extraordinarily fortunate to end up in that little crater, where they could get some nearly-immediate scientific results. Had they landed on the plain in between, they probably would have ignored the little crater and headed straight for the big one; and though it looks promising, that might not be a better scientific 'target'.
I just read an article that indicates they think they can get around a 200-sol lifetime out of each lander, so they've still got some time (Spirit is on sol 78, Opportunity is on sol 57).