Like you, I did a 10-day Veneto-only tour once and have no regrets at keeping it that focused. We did go to Treviso and really enjoyed it. It's very pretty and more laid back/fewer tourists than the other towns you have listed. We had a great day trip of just wandering around the town, and I recommend leaving it on your list. Question for you, though. Your NE Italy itinerary only includes Veneto. Is it just due to time constraints, or do you not have any interest in the other two NE regions? No Trieste or Dolomites? It's tough to narrow things down, I know, but you called it a NE trip, not a Veneto trip, so I was curious.
On our trip, we spent almost no time in Venice, as it was July and boiling hot. All three of my family members got heat exhaustion and were throwing up the two times we tried, so we gave up, abandoned my prepaid vaporetto and museum tickets, and beat a retreat to the countryside. We enjoyed slow-touring Portogruaro, Padova, Treviso, Verona plus the two abortive half days in Venice. I would have liked to have added Vicenza, Brenta Canal and Bassano del Grappa but time ran out. Maybe also something along the coast other than Venice.
I'll return to Venice to see it properly in the off season someday.
My next trip to Italy was Piedmont-only, and I enjoyed it even more. I love your approach.