"I dont doubt there's value to be had in an array of small craft - but to be honest, 3 big assets in geostationary orbit on mars would, imho, be much more worth while."

Why not put 2 craft at Mars' L-1 and L-2

With one in L-1 it could handle all communications for anything on Mars during it's daylight. It would higher in Horizon for more of the planet than compared to geo orbit. [And with extra fuel it could even change it's inclination {to say to a polar orbit or other Ls} to fit special circumstances.]
Putting the spacecraft into L-1 or L-2 should require less fuel than compared to any other orbit and mantaining it's orbit should cost less to stationkeep.
A craft in L-2 would cover most of Mars during the nite.

OR you could use L-4 and L-5. This allow both satellites to share coverage for day and nite. These orbits are more stable than L1&2 and could slightly reduce the time blocked when Mars passes behind the sun.

Upon looking for some reference to find distances of Mars' L-points, I instead found PDF which describes a Mars communication relay Satellite using L-1 & 2:
http://www.stk.com/pdf/white_papers/0701_trajectory_sensitivities.pdf