I've been there and it's a must-do if you like techno. The place is great, perfect for a techno festival with it's post industrial structures.
Actually it's not true that on the other 3 stages there are smaller djs, big djs are on every stage. Just to mention a few, names like Adam Beyer, Sam Paganini, Amelie Lens, Ilario Alicante, Hot Since 82, Paco Osuna, Robert Hood, Pan-Pot, Rodhad and Adriatique were not on the Main Stage last year. I'd say that all stages have djs of the same size but as lineups are not that different every year they just rotate. Also the times they are playing is not related to their size. Solomun was playing at 7:30pm, Luciano at 3pm, Martinez Brothers at 2:30pm, Amelie Lens at 4pm, Timo Maas even at 1pm. You just need to go early and live the whole day if you don't wanna miss anybody.
The worst part is the heat. Except the main stage, other 3 stages have no shade and partying in July under sun can be hard.
After the festival there are several afterparties with Djs of the festivals in clubs like Audiodrome, Big or Milk, so actually the parties don't stop at midnight if you don't want to. Last year afterparties were with names like by Joseph Capriati, Ilario Alicante and Sam Paganini, so big ones.
Turin is a wonderful city, reeeeeeally worth a visit. No campsite, so you'll need to look for an apartment or a hotel.
Don't know if it's an info that interests you or not, but worth a mention that there's police with dogs after the entrance, so after you're in you'll have to walk close to the dog. This happens when they have already checked your tickets. It's something you'll find out only once you're in so keep this in mind.