A solution to Xypherous' statement about vision upgrades being mandatory
Just make them like trinkets; you are unable to purchase them until a certain level. Peharps level 11, or level 16? A support is very unlikely to be at level 11 during the early game.
This way, support players do not have to have the feel that they are mandatory purchases, since they couldn't purchase them anyway.
This would allow Sightstone to finally have its so deserved upgrades, without both them being mandatory on supports and OP on junglers.