Longer wavelengths need longer antennas....
This might turn out to have been too ambitous for a Mars Express class mission, but let's wait and see... Maybe we'll end up needing a MIMO with some more robust antennas.
Mmmmmm...donuts, I mean ....Mars Icy Mantle Observer.
Sound the entire planet with a few plane changes, spend more time over areas of interest, even probe the moons and possibly sputter on to an asteroid or two. It'd be an interesting test bed for VASIMR helicon thruster propulsion system as the RF power electronics could pull double duty.