The problem with Mars exploration is that it seems to usually be the case that the next spacecraft to be sent there is already designed before the last-launched spacecraft has even arrived, let alone after the most recent mission has arrived, sent back data, and resulted in new hypotheses for testing. Certainly true regarding Phoenix and the Mars Science Lab.

It would make more sense to divert some money from Mars exploration to other space science projects where science is ready to try out some new ideas from last mission there. The political issue is that there's a political will to spend money on Mars, but there may not be the political will to divert that money to space telescopes, a Venus mission, or something else.