I can't give any advice or suggestions about must see stops from Perast to Orebic. (We really enjoyed Perast, BTW.) However, I'd like to suggest, based on firsthand experience, not to miss Dubrovnik. It is a beautiful city in a stunning location! We were there this past September. Yes, it was crowded, but I can honestly say the crowds did not detract from our enjoyment of Dubrovnik and it did not detract from its beauty. We weren't bumping into people and we didn't have any long waits. We started walking the walls by 9AM. There were people on the walls, of course, but it honestly wasn't horrible. We were able to go at our own pace. We visited War Photo Limited, the Franciscan Monastery, and took the cable car to the top of Mt. Srd, and did not encounter long lines or horrible crowds. We did not have to wait very long at restaurants (about a 10-minute wait at Kopun, and they gave us a complimentary drink as we waited). We did have advance reservations for Taj Mahal (Bosnian food).
It's your decision, of course, but we loved Dubrovnik, and we think it is definitely worth seeing. I thought Seville in September was much more crowded, especially with tour groups, than Dubrovnik. You can always check the cruise schedule for Dubrovnik to see how many cruise ships will be in port that day. To be honest, I didn't do that because we didn't have a lot of flexibility. I think we only saw one cruise ship in port when we were there, but I'm not 100% sure.