One thing about the spiders is that when the frost all ablates, what is left looks just like sand dunes. So either the spiders are caused by the fact that dunes exist, or dune-like mounds are built largely by "spider" action, or more likely some combination. The Mounds/dunes are modified by both winds and focussed defrosting.

That means that you couldn't prove that dunes anywhere on Mars were caused by spider action (or not). Indeed, there might be a solution here to the fact that most of the dunes on Mars are immobile - too coarse grained to be moved in current winds. If most of their construction was by spider-type focussing of degassing, then they could be built anywhere that thick snow deposits form.

We still have a lot to learn about Mars!