St. Mark's Basilica - Venice

I can't answer the first question as I have never gone to the trouble, although I have also never been there during prime tourist crunch. I suspect they will just tell you to get into non-reserved line. Then again, they may be in a good mood and like you and just let you in.
My experience on photography is that is nearly impossible to enforce given the wide variety of nationalities of differing cultures fiiling the basilica. Doesn't mean you should do it though. Flashes are annoying inside the rather dark basilica, and not very effective given the large space.
The only place I know of where you will definitely get the boot is the Sistine Chapel.

Last October while I was in the Basilica I noticed folks taking pictures outright, even with the Basilica staff walking around. The only picture I wanted where of the original 3 horses. I did so with no flashes, they came out great, and security was just sitting there. From what I observed those taking pictures weren't from the annoying individuals that were posing in front with the "Peace" sign or using the camera sticks.

Wait the rule is no photos and you choose to ignore it? Why?

We arrived 20 minutes early and were let in no problem, they seemed rather loose on the scheduled times. My daughter was wearing shorts and was asked to cover her legs, a scarf she had for that purpose was fine. I did see staff chastising photo-takers, but nothing more than "no photos!"

In most of Europe, including St. Mark's Basilica in Venice, we have noticed that most people do not follow the no photography rule and no one says anything.

We highly recommend paying to go to the museum located on the second floor. It gives you access to the balconies with great views of the square and you can see the original horses as well as their replacements up close. Also allows you to see some of the beautiful gold mosaic tiles closer up.

Sorry if this sounds harsh but why would you be late? You know what your entrance time is-plan accordingly.
As to photos- just because you might not be fined for doing so (and I wish immediate fines could/would be handed out) why would you do something that could potentially damage the artwork?
Sorry but I just don't understand what some people don't undesrtand.

WRT picture taking, I find it really annoying when people flaunt the rules and make a nuisance of themselves while trying to get the perfect shot. You will soon realize for yourself that the tourists taking pictures in these congested tourist sites are a big nuisance for several reasons... Why not buy one of the many souvenir books that have professionally taken photographs? Not only are the pictures much better that you can take given the the lighting conditions and circumstances during your visit, the profit on the souvenir helps pay for the maintenance of the site.

Why not buy one of the many souvenir books that have professionally taken photographs? Aside from the cost, they are usually heavy and after buying them for 2 or 3 sights, the added weight is a burden you have to carry with you for the rest of your trip, then worry about overweight on the flight home.

Re: Chani. Okay, a postcard or two. Not so heavy.

The no photos rule must be new. When we were there in 2008 and 2013 we had no problem taking photos (no flash, of course).

I was there in 2008 and in 2010. The no-photo rule was in effect. In Oct. 2008 the guards seemed to be enforcing the rule. In Feb. 2010 everyone was taking photos and the guards ignored them. Except in the Sistine Chapel, the no-photo rule enforcement has always been sporadic wherever I've been. Oh, just remembered, it was strictly enforced in the synagogues (Venice, Florence and Rome). In Florence I was told that it's Italian law - no photos allowed in places of worship. Maybe that's true.

We arrived a few minutes early for our reservation and they had no problem letting us in. Wise to make a reservation as there was NO line at that door in mid July and at least a 2-3 hour wait without a reservation. There are signs everywhere that say "no photos." I am a rule follower so we followed the rule. I also agree that paying the extra 5 euros to go upstairs to the museum is worth it. We ended up finding a shading spot on the balcony and enjoying the view of the piazza below for a LONG time. Very relaxing! :)