Make middle a capture point instead of 2 seperate buffs, you can capture it just like the other towers across the map but it doesn't fight back if you stand around it. It would take a single person around 15 seconds to capture from neutral, each additional person channeling would reduce time needed by a little bit. Capturing gives everyone on your team the buff but make it slightly weaker than it is now in terms of how powerful the shield is and how much damage the attack is, maybe make it recharge a tiny bit faster.
The tower would become first activatable at 3 or 5 minutes into the game, so it's not just everyone rushes there right from the start.
The buff would be changed to persist through death, and you could tell how long is left on it because the middle tower slowly ticks down until it's neutral again. Once the point is captured, it can't be captured by the other team until its duration runs down and it becomes neutral again, that way not everyone is always middle all the time either.
I think this would encourage more teams to want to go mid and really want to keep control of that buff, right now it's just whoever gets it gets it whenever they want to walk by it.