JonBcn, the qualifying of Zurich does not take place in the main stadium, but rather in some randomly placed courts near the car parking way down town. Last year, Caz & I tried to go and see some of the qualifying that was taking place on Sunday, and by the answer they gave us, I got the feeling either crowds are not welcome or they are completely banned. But if you are nearby I guess you don't lose anything for giving it a try.
And may I add, Zurich is the MOST boring tournament I have ever been to. Sorry, but it is. And I didn't even had to pay for tickets most days. I am not going back even if they give me first row tickets and a VIP badge.