Hey fanofmumbai,
I had almost a similar routing to you just last Christmas, going from BOM-ZRH-YUL. My flight landed at 6:15 in the morning and my outbound flight left at around 13:00. Since both legs are on Swiss they will most definitely check your baggage through to BCN as its a just a really long layover, so you shouldn't have to worry about your checked baggage.
As for traveling to downtown Zurich, its very easy using public transit. Here is some useful information directly from the Zurich Airport site that helped me get to downtown:
"If you have a wait of more than 4 hours, it’s well worth paying a visit to Zurich. There are 6 trains an hour from the airport to Zurich main station. The journey takes 12 minutes and costs CHF 12.40 (return fare).
Follow the “Exit Zurich/Baggage Claim" signs, observing the entry and customs regulations."
Also I believe the frequency for the trains back to the airport is the same, my advice is to just check the timetable when you get into downtown just to see what times the train goes back.
As for when you get into downtown(hopefully you're not flying in on sunday as most if not all the shopping stores are closed) it will be a short walk to Lake Zurich, and you can indulge in whatever else you want.
I hope I was able to help
(PS I thought my first post on FT was definitely going to be a question not a response lol)