NicK this is a very interesting comment. But if the surface of Mars is a thick layer of fragmented rock, then the existence of a surface layer of sulfate rich rocks surely implies that were a "recent" addition. This why I for one do not believe the much-hyped hypothesis that the sulfate layer was formed in flowing acid-sulfate waters at some x Gy period ago.
Similar sulphate layered deposits were seen by Viking 1 and there is a suggestion even Spirit may have seen some; i.e. it is a global not local feature of the surface of Mars. Further, it is a soft material, which erodes even in the gentle winds of Mars. This is why I just don’t believe the NASA model that has been exposed after burial to 1 km by other sediments. (Why would 1km of basalt erode away to expose such a soft rock?). The 1km of burial is needed to convert goethite (what you get in low temp acid saline solutions along with jarosite) to hematite (the blueberries). But if that water hypothesis is also to hold up, other geochemistry must follow.
You have mentioned the sabkha model but a feature of that environment or other acid saline solutions leading to jarosite formation is that other metals eg Cu, Ni etc are also carried in solution and co-precipitated with the jarosite. If NASA would tell us how much jarosite that has been measured in the sulfate layer, then we could see if the other metal concentrations are in accord with the hypothesis of formation from solution. IMHO, the alternative model that the sulfate layer represents recent (i.e x00 M yr) volcanism or cometary impact is more in accord with the jarosite + hematite composition of the surface. The uniqueness of the Meridani area is probably indicative of it being near to the source.
This model calls for a possibly unique event but they seem to occur frequently in the solar system (eg the impact that formed the earth-moon system, etc). But I fervently support your comment that Mars is Mars-like and should be treated as such. One year ago we saw a war commence because remotely-sensed images were interpreted by belief instead of by reason. Let Mars not suffer the same fate.