Either way, Venice is NOT conducive to rolling suitcases. Vaporettos & water taxi's & Traghettos, steps over bridges, cobblestone walks, very narrow walkways/doorways.
Bags with backpack straps are FAR better.
Jim
Totally disagree. Spent 5 days in Venice this last May, before our 7-nite Eastern Caribbean cruise to Greece (Royal Caribbean, Splendour of the Seas), followed by a week in Rome. Although the DW had a small carry-on and I used my backpack as a personal carry-on, we did check-in a roll-up garment bag (cruise ship stuff), along with a large 50 lb baggage filled hard-shell, spinner, Samsonite suitcase "with wheels". The only trouble we had was getting it, our other baggage, and my wife, off the water taxi from the airport at the tiny staircase at the Hilton Molino Stucky in Venice, no dock.
I placed the roll-up garment bag on-top of the wheeled suitcase and it was a life saver, just push and go.
Don't know if you ever switched planes in Rome from the International terminal over to Domestic, but it is a long walk.
Don't know if you ever carried baggage from the Venice cruise ship terminal and Piazzale Roma over to the train station, but it is a long walk. Granted it was a pain getting the suitcase up the bridge without a ramp, but the wheels were a life saver.
Don't know if you've ever been to Europe for 3 weeks combined with a cruise for 7 nites, but you can't make with just a backpack as you stated: wheeled suitcases are a necessity.