No, there would not have been other rovers on Mars in the meantime. There were no rovers in development between MER (Spirit and Opportunity) and MSL (which is

No, there would not have been other rovers on Mars in the meantime. There were no rovers in development between MER (Spirit and Opportunity) and MSL (which is now en route to Mars). There's a lot riding on MSL landing safely, because there's nothing solid after MSL right now. There used to be a 2018 rover, but it was recently cancelled.