Is it worth it to get the Dubrovnik card? A 3-day costs 180 KN, and the wall alone has now gone up to 120kn. Not sure if the other destinations are worth going to, but they seem worthy. This card also gets you public transport - would we use it? We're staying in the old town before heading out to one of the islands for a few days. I've gotten these before (I'm talking about you, Paris) and been disappointed to learn that the places we wanted to go to were not accepting the card.
You need to tally up the costs of the attractions you want to see, along with price (and check if they're covered), to see if it's "worth it". I stayed in Old Town but used the card to get to the main bus station to take a long-distance bus to Split. Public transport is inexpensive though, so that would not be the main draw.
I say go with the card. You do not need the 3 day card. Get the 1 day card. Don't get it ahead of time - you can get it in several places in Dubrovnik, and there is no wait. There is a small shop right by the Pile gate (N gate of the old town) that sells them. Very simple, and quick. Even when there are hordes of tourists, easy to get. And go to the Buzz Bar for coffee. If you do, tell them the American with the black hat sent you.