If mission rank exceeds your rank you can still take the mission but you will not get the material rewards as listed on the mission outline. Especially for CIF, MEF and EFC and other really rare stuff.
Are you sure? Any official statement from FD regarding this? I've never experienced that.
You're right Starman it's pure nonsense, sure you're getting also the commodity/material rewards from missions if the mission ranking exceeds your own rank.