Dust Devils on Mars

I've heard in some of the press conferences questions from the press about
concerns for potential dust devils in the vicinity of Spirit. The response
to the questions was something like: the MER is heavy and could not be
tipped over by the dust devil. I think this misses the point. I'd be
concerned that the dust devil would churn up so much dust that the solar
panels would be seriously degraded. I suppose dust devils come up so
quickly that it's an unavoidable, but remote, possible hazard. I did
wonder, though, what the prospect is of an "emergency folding" of the solar
panels...

How much extra could a couple of "windshield wipers" have cost in weight?
:-)

Jon