Well, Treviso is lovely and interesting, while Mestre (from what I've read on this forum) is not. We had a car while staying in Treviso for 6 nights, so we just drove to the airport on the morning of our flight home --- I wonder if you could arrange for a taxi. It's at least an hour by public transportation, with one change, but not even half an hour by car. Sometimes there is a shuttle bus from the Treviso train station to VCE. We stayed in an apartment in the oldest part of the town, so I don't know about hotels or B&Bs.
On our Veneto trip, we did greatly enjoy going up and down the grand canal on our way to Chioggia and back (I do not recommend that town although we had a good lunch there) --- it was fun even though we've spent 2 weeks in Venice on previous trips. Also appalling to see the crowds at San Marco and Rialto --- we were glad we were just breezing by them on the water!
Treviso has canals and bridges, plenty of great places to eat, frescoed Venetian-style buildings, old city walls, interesting small churches and museums, a fish market on an island, some cool wire mesh art installations on some of the walls of the buildings, and many pedestrian-only streets and porticoed sidewalks. If there were tourists there, they were Italian.