Which month are you going? If you want to be able to swim for example, late May would be the earliest for me.
It would almost 99% depend on flight options for me. There are plenty of good options in Croatia, but if you wanted to fly to Venice after another day or so in DBV, then fly to Venice for the rest and fly home from there, that sounds like a fine idea.
Near Dubrovnik, you could dip into Montenegro or Bosnia (both I would do with a car, but not vital), or go back to Korcula (via Peljesac, where you can do wine tasting, stop at Ston). Or you could head north to fly out of Split and stop over on Hvar or another island. You also could spend time on the islands off Dubrovnik--that's definitely a "get away from it all" kind of vibe. You could head to Zagreb, which the tour skips, and do a bit of exploring in the north--Varazdin always looked pretty to me but I have not made it yet.
Or, you could play around with Skyscanner and see other cities you could fly to and then get a good flight home from.