Ok, Just a stop-gap idea, or maybe it's a good one... don't know. Lower the prices of lower-tech items as high-tech stuff gets researched. Mostly this is for Tank Chassises, but essentially, when you get the med chassis, the light chassis goes down in price. When heavy is researched, med and light go down. This will help balance out the med-vs-heavy conundrum, as well as the "Noob eating res and not letting you get a proper tank". If you get the expensive heavy, the noob will be "well, I can't afford a heavy tank, so I'll just get a light, since it's a lot cheaper..."
Compaired to Heavies, Lights are already very inexpensive, and for NF still effective, is properly handled. I think even if they were free, it wouldn't encourage people to drive them. When heavies are avaible, no one wants to drive a dinky little light.
Hey man, I took off 5 plates of compo on a rail heavy with an LT, against one of my own clanmates, kieshdor still killed me, but damn I hit him hard.