I'd like to see plug n play rovers.
The MER rovers (as well as the airbag landing technique) have proven themselves to be extremely rugged and reliable. They should keep this design and begin developing a whole line of instuments to be carried and used by future missions. The rovers could be outfitted for specific tasks depending on the goals of the mission. When the findings of a particular mission raises new questions, then another rover with different instruments can be sent to answer them. Too much solid engineering data has been acquired over the course of this program to not be reused and thrown away.