Is this doable??? Krka from Split in the morning, drive to Plitvice in the afternoon?

This is all very rushed - I think you are aware of that.

Krka and Plitvice are different kinds of parks. What do you want to see at Krka? There are a number of things that are spread out - a couple of waterfalls, some Roman ruins, etc. Many people I suspect (including me, anyway) see only the big Skradinski Buk cascading waterfall at Krka. You can park your car at Skradin and take a boat up to Skradinski Buk and back. It's a huge falls, dwarfing any one waterfall at Plitvice. But you need not see EVERYTHING at Krka.

Plitvice is a more coherent hiking experience. There are lots of little waterfalls, sometimes around every bend on the trail. But you can see the gist of the park in a good 6-7 hours.

Could you do both? Yes - I'd probably see only the Skradinski Buk and then move on. Stay at one of the overpriced park hotels at Plitvice so you can easily get into Plitvice at 7am when it opens, to maximize your time without the crowds. You might even stay the night at the town of Skradin instead of in Split (spend a few hours at Diocletian's Palace and move on to Skradin by evening). I suppose you might even get to Skradinski Buk by afternoon from Split and drive late up to Plitvice (2-3 hours?) and get into that park first thing the next morning. That would be a real whirlwind trip though.

(If you want to see Skradinski Buk the following morning instead...another town to stop in might be Sibenik, a lovely town on the other side of the highway from Skradin. Obviously, on such a tight schedule, you won't be able to see everything.)

It's a shame you're bypassing my favorite city in Europe, Ljubljana, between Zagreb and Venice. Consider taking two nights there - train from Zagreb to Ljubljana, then take a bus or transfer service (or if you like trains, a train via Trieste that will take longer) on to Venice. Ljubljana is charming, delightful little city that has tourists now but nothing like the mobs at Dubrovnik, Plitvice, or Venice.

You must not ever leave anything visible in your car. Everything should be stowed away in the trunk before you pull into the parking lot. I would not leave pricey electronics even in the trunk.

As usual I will follow up with Andrew and recommend a couple nights in Ljubljana. Our favorite city in Europe thus far! So glad you have included Korcula. Can't think of a better place to spend an anniversary! 2-3 nights are perfect. Our favorite island. We had a memorable dinner at Nonno overlooking the water. It was magical! You might reconsider skipping Zagreb for Ljubljana. We had actually started in Venice and took the GoOpti Shuttle to Ljubljana. A comfortable, convenient 2.5 hour ride. This could be an option rather than flying out of Zagreb?

I forgot to respond to the question about leaving stuff in the car. I visited both Krka and Plitvice on my last trip to Croatia (not back to back however). I parked my car at some sort of makeshift parking lot ("free parking if you buy something at one of these restaurants") without issue. All of my stuff (laptop) was in the trunk. But it was not a big lot, and there were enough people nearby (including an attendant) where I felt safe leaving it there.

At Plitvice, I parked in one of the big official pay lots. I don't know how well patrolled it was. I suppose my stuff was at risk, but I didn't worry about. As said above: never leave anything valuable visible in the car, at very least.

Thank you! I like that option! We are only going to zagreb to catch a flight to venice. if this is a viable option, it might work! I'll look into it a little more, or if you have any more info on it that would be great!

thank you for the suggestion for the restaurant on our anniversary on korcula!

hmmm . . . didn't realize Ljubljana isn't in Croatia. we'll be renting a car from split and really don't want to have to return it in another country. plus it's an extra hour farther than Zagreb. with our itinerary, i don't know if it would be worth it because we wouldn't really have any time to visit.

But on that note - is there somewhere closer than going to Zagreb after we leave Plitvice (in Croatia) that we can catch a ferry to Venice instead of going up to Zagreb?

Yes, Ljubljana is in Slovenia. It's about 2.5 hours by train from Zagreb to Ljubljana. Return the car in Zagreb and take the train.

If you don't want to visit Zagreb or Ljubljana, you could head to Istria and return the car there, then take a ferry (from say Rovinj, Pula, or Porec). I loved little Rovinj, Pula not so much. Didn't visit Porec. Yes, you can drop a car in Rovinj, but there aren't a lot of agencies. Try EconomyCarRentals or Auto Europe. Otherwise, some of the bigger car companies will force you to drop in Pula, maybe at the airport.

wow, just looked into my intinerary a bit more. there's really no viable option that doesn't take a whole day's travel just to get from zagreb (or any other area nearby). buses, trains, ferries, all take a whole day. there's no direct, non-stop flight!

that being said, we are very flexible right now as I haven't booked my flight yet from US. so now re-thinking maybe better to go the opposite direction - fly into Zagreb and fly out of Dubrovnik to Rome. and then do our opposite itinerary in Italy too, ending in Venice. there's a few non-stops from Dubrovnik to Rome. Any thoughts on this? Am I missing something?
Thanks!