On our last visit to Venice we did a tour of the Clock Tower (Piazza San Marco). Very interesting and great views of the Piazza. We also did the Secret Itineraries tour of the Doges' Palace which was also very interesting. And for us a highlight of Venice was the Peggy Guggenheim Collection.
In Koper, we took the public bus to Piran - a lovely, well preserved, medieval Venetian port town. Piran is considered one of the most authentic/most photogenic towns on Adriatic coast. It's a beautiful setting jutting out into Adriatic.
There is so much to Dubrovnik than the walls. Don't get me wrong, the walls are awesome in the true sense of the word, but there are so many gorgeous, most often overlooked, details which are fascinating. Don't miss Gundulic Square at noon!
We did a private morning tour (Tours by Milo) when in Kotor and visited places and were imparted historic details. We then wandered Kotor on our own in the afternoon. We didn't visit, but there's a Cats Museum!