I thought we knew all that, to be honest.
We've detected river beds, lakes and other evidence of standing and running liquid water before. The technology, except for the landing, doesn't seem to be a giant leap forward.
I do like the idea that it's practice for more robotic work, and considering the miniscule cost compared to one stealth bomber I don't begrudge them the experience even a little bit. But from an ignorant point of view it seems, appears, to have had limited value on the way to new knowledge.