Why not insist on 1 gee at 1 RPM? Not many (if any) tests of
spin-generated 'gravity' have been done but the consensus seems to be
that 1 RPM won't induce nausea in most people while 3RPM might. Also,
if we give the crew 1gee for the transit to/from Mars, they'll only be
exposed to 0.38gee for the time they're on the surface (a few months?).
We know people can take zero-gee for a year. Why waste a year or two
testing people in LEO at Mars-gee?

The cost to design, build, and test a 1 mile tether system won't be
significantly greater than the costs for a 76m system. Maybe less, if,
for a 76m system, you have to design measures in the crew quarters to
deal with high Coriolus forces.