Nine days in Croatia in June

If you don't plan on hitting any beaches in Dubrovnik, your time frame is enough. But the beaches here are beautiful and you wouldn't want to miss out on that. 1 full day to explore the town, do the walls, and do the gondola up to Mount Srd should be enough, but that's all you would be able to do.

Plitvice will always outweigh Krka, but to do that in half a day, plus driving from Split and driving to Pula afterwards is definitely suicide. But I'm not sure if you meant to spend the night near there (or Krka) and continue on to Pula the following morning.

I drove from the Pula area down to Split last year. Part of the drive is on the local roads, which means lots of stops. But once on the toll roads you can basically fly. I know I was going way over the posted speed limit (I must have been hitting 90 mph on the A1 at times) but I never saw any police and I never got pulled over.

I visited Pula while staying in Rovinj. I arrived in the morning and spent maybe 2-3 hours there, but you can probably do it quicker than that. For me, personally, I probably could have skipped it, but if you haven't seen the Coliseum in Rome before then Pula is worth a look for their amphitheater.

We were thinking that we would drive from Split to Plitvice in the afternoon, spend the night nearby, do the park after breakfast, and then drive to Pula in the afternoon. But now we're thinking we may return to Split and fly from there to Venice. Plitvice-Split is going to be an easier drive than Plitvice-Pula, yes?

We've actually been to the Colosseum in Rome. The one in Pula is a mini-version, right?

Use Split as your launching point for seeing islands. You don't need a rental car to get between Dubrovnik and Split (lots of nice, modern, inexpensive buses running that route along the Adriatic), or to see the islands (it will be an expensive impediment). Save the car for Plitvice for when you really need it to maximize time savings.

Trogir is smaller and more laid back than Split. Split is simply much bigger and more stuff to do - you should allow at least 1 day or 2 to see it, it will be worth it. Depends what you're interested in, but Diocletian's Palace is a must. With a side trip to Trogir, that's already at least 2.5-3 days.

Dubrovnik is very compact - 1.5 days will do if you just see the fortified city and some attractions.

As far as the islands go, the ferry schedules will determine what you can do. I found that I wasn't able to squeeze in as much as I wanted because there was no same day return from say, Korcula (however, I went in September so that may or may not have something to do with the frequencies).

Your plan to drive up to Plitvice during the afternoon and exploring the following day sounds like a decent plan. But yeah if you don't feel the need to go to Pula then perhaps go with your other plan and fly out of Split. I only know the drive between Split and Plitvice (not Plitvice to Pula). The majority of the route is along the A1, so it's a really efficient and smooth road. Then you need to make your way to a local road for the final leg to Plitvice.

And yes, if you've been to Rome already you don't need to see the mini version of the Colliseum in Pula. There really isn't much to see there in my opinion (but that's just me).

Agreed with previous post, take a bus between Dubrovnik and Split. It will save you lots of money. Gas is prohibitively expensive in Croatia.

No Pula for us as it turns out that the Split-Venice flight operates on the night we need. We are going to rent a car, we like the convenience and freedom and we'll insist on a diesel if they don't give us one in the first place. We'll drive to Korcula -- should we spend two or three nights? -- take the ferry to Split, stay there or in Trogir, and then do the trip up and back to Plitvice.