What we know with certainty is that life in the universe is rare, as far as we know earth is the only planet that has it.
That's total nonsense. And you contradict yourself in the next sentence:
Everything else about life elsewhere is simply hypothesis and statistics, but unproven.
We know nothing about life in the universe. Nothing. Zero, nada, zilch, null. Until we have a much larger data sample, it is all just theoretical. Completely true, and until the intervention of interstellar travel, unavoidable.
That is exactly why we're looking for any clues we might find. That includes not only Mars, but also Europa, for example, where some scientists believe we might find primitive life.
We know for sure that there's life on Earth. We can exclude most of the other planets and moons as they can not possibly sustain any life based on anything we can imagine.
But that's just the solar system. For the rest of the universe, we have, for example, just recently changed our estimate about how common planets are. We thought that most suns wouldn't have any, now we think almost the opposite.
We have just started having methods to find planets of earth size.
But still, life somewhere else in the solar system would be a pretty big deal.
Intelligent life is even rarer, given the biomass of earth.
Wrong. Biomass is not the deciding factor. Right now, our sample size indicates that 100% of planets with life at all will bring about intelligent life. But that could just be due to the anthropic principle. We don't know if Earth is a rare exception, or if there's something to evolution that will result in intelligence in most cases.
Again, getting closer to an answer here, in either direction, would be a pretty big deal.