What was your best classical musical experience in Venice -- not necessarily limited to Vivaldi. While I know to avoid the costumed performers (generally true, I'd guess), I'm not sure how to narrow the options beyond that. Thanks.
Go to a performance in a location you can actually find in the dark, and that is happening on a night you are available. If you are a musician, or really know great from not-so-great music, it probably makes a difference which performance you attend.
One of the highlights of our most recent trip to Venice was a shoestring budget performance of La Boheme at the Scuola Grande di San Giovanni Evangelista. The casting is a role of the dice, but the Mimi in the production we saw could have been on the stage at the Met, so amazing was she. The singers were from the chorus of Teatro La Fenice. The orchestra was made up of about 7 or 8 musicians. Here's the link: http://www.scuolasangiovanni.it/index.php?page=35<=en