Just back from Pula and it's really nice. it's got a massive amphitheatre - they put on gladiator shows, it's worth checking to see if you'll be there when they are on. We also did a boat tour out around the islands (was about 25e for 3 hours including food and wine). It's a small place and you can easily see everything in 24 hours.
The airport is a bit frantic though - lots of queueing if you're flying on a sunday morning. Buses to the airport are a bit of a hassle - we had a look at them and decided to get a taxi instead for 20e.
PS: If you're in Dubrovnik and have the time, a day trip to Kotor in Montenegro is worth looking into