Scientific return isn't something that can be planned, or it can be planned only tentatively. If surprising results appear they should be able to cause the plan to be radically changed or abandoned. Surprises are a sign that we're getting somewhere, but NASA doesn't like surprises or changes of plan.
Are more sample analyses more scientific return? Maybe, but if they don't contribute to a greater understanding they haven't really accomplished anything. I think that there is no chance at all of sorting out a clear history of climate or sedimentation by testing the rocks of Gale Crater, because Mars science just can't change enough yet to accept a big early discovery of Oppy's: The layered deposits are impact sediments. The floor of Gale has really interesting looking sediments but unless we switch paradigms they might as well be white noise.
Here's another example of a result that should have changed the plan:
What is all that native soil disturbance in the upper left corner of the image? Its a big surprise along with hundreds of other examples at Gale and both MER sites. I'd abandon the plan and start studying this unexpected activity.