Multiple flights Barcelona/Venice/USA

How much time do you have between flights on the 11th? What if your VCE-BCN flight is delayed? Will you have your boarding pass for your US flight when you leave Venice. I have not been in your situation, but I suspect you will need to get a boarding pass for your US flt in BCN

If you check a bag you will need to retrieve it, check it in for your US bound flight , go through security and "passport control etc"

Without any other specifics, if there is less than 4 hours between your flights , you may want to have antacids handy on the 11th.

Thanks for the info! Nothing is booked yet (we may just get a very late flight on the 10th instead), but if we end up going with this idea, we'll have about two and half hours between flights. Delays happen even when there are layovers on a flight booked the more "traditional" way so I just accept this as a reality whenever I travel; is there a reason besides delays that you're suggesting leaving four hours in between flights? We do plan to check in for all flights in advance and have all of our boarding passes ready to go before arriving at the airport, and I would definitely prefer to not check bags so as to avoid having to recheck bags in between flights.

When flights are on one ticket, a delay in the first flight may cause you to miss the second one, but the airline is responsible for getting you on another flight. With separate tickets such as you propose, if you miss your home bound flight because the flight from Venice is delayed, you are responsible for getting a new ticket---often at considerable cost.

I would not take this chance before a long-haul flight; I would fly in the night before.

Lola makes a very good point about the distinction of multiple flights on a single booking( ticket) versus 2 independently booked flights.

Where you proposed having 2 bookings, if your first flight is late and you miss the 2nd flight, you are stuck for buying a new ticket at "walk up" prices. Thus my suggestion of at least 4 hours to build in a little fudge factor, should your first flight be late, lines are long or you have to hunt down your luggage because someone out it on the wrong carousel, etc.....

A little bit of boredom waiting at the airport is free ( or only the cost of a glass of wine!) where missing the plane gets really expensive.

Its your money, so its really a matter of how comfortable you are, in placing your "bet"

Ok, that all makes perfect sense-- thank you very much Lola and Joe! Looking at our schedule and available flights out of Venice on the 10th, it doesn't look like we actually lose much time by leaving on the night of the 10th as opposed to morning of the 11th, and the extra hotel for the night should fit into our budget. I'm not opposed to buying some peace of mind once in a while!

It's hard to give flight advice if we don't know what your home airport is.
And why don't you look for Open Jaw tickets into one city and out of another? Backtracking is inefficient and it can add substantially to your travel costs--both directly and indirectly.
It's always preferable to fly on one ticket and one airline if you must transfer to another flight to get home.
We always carry on our luggage--even if traveling for 3-4 weeks at a time. Just follow Rick Steves' packing list with minor adjustments.

How is it an "extra" hotel night?-- you were going to be staying somewhere. either Venice or Barcelona, right?