I expect that at some point in a later mission extension, the mission on Earth will be reduced to a group of three grad students, two minutes a day from the Deep Space Network, and a lot of auto-navigation [very low sustainable budget].
With luck in a year or so, Spirit will have climbed all of the Columbia Hills, getting good science from numerous outcrops, and a year beyond that it could be making its way to the nearest Gustav Crater wall. As to Opportunity, eventually it will have seen everything there is to see in that crater. It will investigate where the heat shield crashed, and THEN WHAT? Drive in a straight line for a hundred miles looking for a place with no blueberries.
Forming opinions as we speak