Is this worth a visit in late November? We are looking for a day trip from Salzburg.
I went through Zell on the train in late August. If you like lake-based activities, you might like it. It is on a large lake. Other than that, I didn't see anything to particularly distinguish it from other lake towns in Austria. It definitely is not as picturesque as Hallstatt.
St. Gilgen, St. Wolfgang, and Mondsee are perhaps a shorter distance from Salzburg.
We stayed in Zell am See 2 weeks ago. We loved it there, although it may be very quiet in late November. We were there the first day of November (it was a thursday) in 2007 and most places were closed. Have you considered a visit to "Mad" King Ludwig's Neues Schloss (Herrenchiemsee)? It's about an hour from Salzburg.
Closer yet (about 30 minutes away) are Berchtesgaden and Bad Reichenhall.