Honestly I think one of the possible premier uses of orbital (though not Martian) resources would actually be agriculture. Limiting biological contamination and maintaining sterile environments, unlike other industries, can produce a value-added product compared to the inputs.

Also there's at least a plausible mass trade off - a space borne habitat structure doesn't need to support its own weight against gravity, so you might be able to trade favorably on the launch costs (e.g. grow crops in a big inflatable dome under hydroponic conditions). Certainly it would make enforcing quarantine easier.

Large structures and LEO do look like the closest you could come to the LEO dream. The atmosphere for a baby Bernal sphere that has a usable area of 35 acres would take about 15 starships to send up which would be like getting 1 starship load to the moon. Building something like that which is a simulation environment for Mars might be cheaper than going to Mars.