Gary,

I agree entirely with actually USING a design we have that works vs spending a huge amount on an pretty shaky concept.

The one point I was making about how MER isn't a direct substitute for MSL is that in some loctions, MER has a 0% chance of a successful mission. High latitudes where it is too dim/too cold, for example. It would also not be suited to missions that require driving more than a km or so (like where satisfying the requirements means visiting multiple locales at a site, or where the conecpt is to land in a safer area and drive into something more interesting). I'm not sure how much the altitude constraints are firm or could easily be stretched (ruling out the floor of Hellas if not, for example).

But for things like winds, rock abundance, presence of some bad patches in the ellipse, sure, let's take some chances!