When fine tuning the lighting in a scene, frequently the director will ask for tweaks like bringing down the spec hit from a light. Currently you can only turn the spec off from a light, you can't reduce its strength. You can create multiple lights, but that can lead quickly to a lot of extra useless lights. I'd like to see the Specular and Diffuse checkboxes in the lights changed to spinners.

For more info (including pictures), please visit here:
http://www.neilblevins.com/cg_tools/cg_wishlist/3dsmax/wishlist_surface_type_multipliers.htm