I think the main issue will be to come back to Buenos Aires. Carpooling will be a good option.
FYI: As you may know, La Plata was designed to be a city before the beggining of the construction projects. It is a perfect grid, so you will be thinking, it is very easy to move around town then but, it has diagonals.... and many people get lost at diagonals. Diagonals are specially at the center of the city, I dont think there are many near the stadium.
The signs on the roads to get into and out of the highway are good... and you will be into traffice jumps anyway.