My idea is that the observatories are used as wards that are contested over by the two teams. Players from either team can put gold into either of the observatories to try to win their power. This power is a light that shines on a certain part of the field giving vision. When a player puts gold into an observatory that player chooses top or bottom, the observatories will shine a light on the according rune spot which is visible for that player's team for 5 minutes or until an opposing team puts in a contesting bid.

-It doesn't matter which observatory is visited, only 1 light can be shone at any time.
-If a rune spawns on the spot where the light is being shone a small sound effect alert should play.
-If there is no lights being shone a player may visit an observatory and pay 50g to shine up a rune spot.
-If your team already has the light, a player can pay 50g to restart the timer on the light (not extend)
-If the enemy already has paid an observatory for the light a player may make a contesting bid of 80g to remove the opponent's light and choose one for him/herself.
-There is no notification when the opposing team makes a contesting bid for the light.
-The light shone is fairly small in radius, around 100 units.

-Before the game starts (at 0.00) both teams may put money into either observatory in a contest for the first light. 10g is added per click at this point. Whichever team put in more money at 0.00 gets the first light. The first light is incontestable until 3:00.

I think this would make a fun element in the game where the players on opposing teams can interact in a new way. Players with excess gold at the beginning of the game can contribute to the first light fund to ensure a slight advantage in obtaining the first runes. Supports on the team with the light can focus on ward placement in other places like anti-gank or spawn block areas. It also gives the observatories a larger purpose in the game.