I have many uses for E gems in late game: endgame troops (Mechanical Men / Living Statues), remote assassination (Living Earth), quick sieges (Crumble), and gear (Earth Boots, Hammers, Marble Armor mainly).
F and W mainly for remote attack spells as was mentioned
A mostly for air boosters as I like to be able to have many casters capable of busting out some Fog Warriors. Also Seeking Arrows are quite amusing.
