People in the ISS staring back at Earth while a huge asteroid wipes off the planet killing off all mammals would probably say "yup... that's some nice ROI.. good investing".
And then they realize that they have all men up there on the current rotation
-- Steven Wright
I'm not saying we expected the rovers to drop dead at the stroke of midnight on sol 91, but even the wildest optimists on the project did not openly dare to hope that we'd even double that 90-sol lifetime.
Actually I was one of the wild optimists on the project, and before landing I predicted that (if they successfully landed and deployed, which was not a given), that they would survive up to solar conjunction in September 2004, or about eight months. More than double the warranty lifetime. I said "Opportunity might make it through conjunction a go a little longer, but I doubt it."
I recall that Jake Matijevic agreed with my calculation -- it was based on his "minimum watt-hours per sol" survival numbers at the time, which he has since improved on by a factor of two or more. But no one on the project predicted survival beyond conunction.
If someone told us five years, we would have laughed. "Impossible", we would have confidently replied
The star of riches is shining upon you.