I got interested again in space exploration and development way back in 1977 when I read a book by physicist Gerard K. O'Neill titled The High Frontier: Human Colonies in Space. That book laid out a case for building large rotating space stations -- called space colonies -- that could be as large as 5 miles long and 2 miles in diameter. By rotating them, it would feel -- roughly -- like Earth normal gravity inside. With a properly created biosphere inside, it would seem like living on Earth. What would the people in these colonies do to benefit people on Earth? One big idea was building space based solar power stations that would power the Earth cleanly and cheaply.
As the years progressed, I learned that such things, if possible, are far in the future. One group I joined was the L5 Society. Back in the early 1980s a common saying was "L5 by '95." We were young and very optimistic. I now sometimes say "L5 by '95 -- 2495." Since the 1980s we have learned we have much to learn about creating independent biospheres. Some of the Mars crowd is working on that. I think that is a good thing -- but it will take a long time.
Could people on Mars -- assuming they could get there -- do anything to benefit people on Earth as much as this? I and others doubt it -- at least in the near term future. Terraform Mars? Please.
All Dressed Up For Mars and Nowhere To Go by Elmo Keep goes into the problems with sending humans to Mars in far more detail than I can do in a short Slashdot post.