Have a lvl40 Evoker, haven't noticed anything that is really needed from the Shop. The sub gives some convenience (like an extra roll at the end of a dungeon), and a box each day with some random crap in it. The difficulty does go up at higher levels, but if you run a top tier dungeon with a group, its not that bad. Yea, the Control tree for Evokers is really high damage, but at max level (52), you might want to grab the fire skill that lays down a big molten pool, it does a lot of dmg over time (Burst skill).