We should get a little more from upgrading Sightstone
All you get from SS to Ruby SS is 150 Health and an extra ward, it doesn't seem all that worth it.
I almost NEVER see Supports upgrading SS, unless it's late LATE into the game and there is literally nothing else to buy/upgrade.
So, I think upgrading from SS to Ruby SS should also increase your total Ward cap by 1. So Supports will be able to place a total of 4 Wards (Pinks wards will stay the same, cap at 1) at a time. I don't think it could really get abused by any means, sure you see Junglers build SS, but I have never seen a Jungler upgrade it. (And honestly, I have only ever seen a Lee Sin buy SS.)