When my suspension was installed, no grease was used on spring metal/metal contact areas, and I would guess not on yours as well. The primary reason, as your question suggests, the grease is not going to remain effective long, since it is not a very accommodating environment for it. Some types of grease will work longer, and you might inquire at a machine shop about that. Basically, most coilover suspensions have some creaks and squeaks that are unavoidable, just like solid bushings. Almost everything you can do to improve the car on track involve a tradeoff for street use, most notably noise and limited life.
2011 Space Gray Coupe, DCT, ZCP, StopTech ST-60/ST-40 BBK.