I think the magic word is Bernoulli Effect here. Causes increased wind speed in the cater and hence greater erosion and cleaning of the solar panels. Also why all the loose rocks have over time been cut down to form the rock slopes we now see and all the detritus originally present after the impact to have been removed. Whilst there has beem much published in the past on wind erosion on Mars (eg work by Leovy), the Bernoulli Effect seems to have been mostly ignored. Endurance shows how wind can carve / deepen a surface feature on Mars and I've been suprised at the lack of comment on it. Still NASA seems to be keeping results from Endurance very close to their chest and this may be just one of those.