I highly recommend Shayler's book: Apollo, The lost and forgotten missions.
It's about countless plans NASA had for the Apollo spacecrafts; not only missed missions to the Moon, but also earth-orbit missions using modified LM versions, like the ATM, for flights lasting up to 45 days!

There was a plan to use a Saturn V for a Polar Orbit Mission (from the KSC!!)
90 seconds after launch, the Saturn 5 would begin a yaw steering manoeuvre to take it on a southerly course over the Caribbean islands. A delay of 100 seconds for the LET jettison was introduced to avoid Cuba. Injection into a 100 x 200 nautical-mile polar orbit would take place as the vehicle flew over the coast of Ecuador, with the orbit circularized at the 200-mile perigee point.

All those plans (except Skylab) were scrapped whenit was realized unmanned satellites could do a better job.
However, many of the experiments thought of in the 60's were realized during Shuttle Spacelab flights, much later.

I'm wondering if a Saturn 1B Apollo flight would have been cheaper than a Shuttle mission....

Raoul