So because they are no longer new, we should abandon the Mars Rovers, Cassini, the Viking probes, and other projects just because they are beyond their mission lifetime?
We should stop measuring lunar albedo just because it's always the same? We should stop the pitch drop experiment? We shouldn't have measured the cosmic background radiation to look for spatial variations? We shouldn't have measured continental drift because it can't possibly happen and mountains don't move? Just because something appears static (and without comparing against previous measurements, we have no means for verifying that), does not mean it isn't changing over longer time scales that are still very important.
I'll repeat my thesis: we are so data-poor about the solar system that the feed from any single working probe is vital. The cost of receiving data is trivial compared to the cost of construction and launch.