Cathy, I wasn't crazy about Split, either, but many others seem to unlike David and me - so who knows? This is one of those "personal preference" questions. I think my expectations for Split were just way too high. I would probably not do two full days there though - one day to explore, one day for the day trip to Hvar (which I've not been to - only to Korcula which I too liked).
To get a good view down on Split, hike up to Marjan Hill, which is to the north of the center (easy to find - ask around).
You might also consider visiting Trogir as a day trip from Split - it's a small town, charming, doesn't take much time to see, almost takes as much time to get there and back as to see it. If you see it the first day of driving, I think it will suck up half of your day with getting there, parking, etc. Instead, I would consider taking a ferry there from Split during your day there - only a half hour it looks like (I didn't take it), probably as fast as driving there. And plan to stop elsewhere driving north from Split.
Some suggestions to stop: the lovely town of Sibenik. And, Krka National Park (which is not far from Sibenik). You could park your car at the town of Skradin and take a boat up the river to Skradinski Buk, a magnificent cascading waterfall (much bigger than anything you'll find at Plitvice) and walk up and around it. Some say it has a similar feel to Plitvice, but I really prefer Plitvice - except for this one great waterfall. You can limit your visit to Krka to just this one waterfall. I did. But there is more to see in the park - much more spread out than Plitvice so more time consuming.
If you are staying at one of the park hotels in Plitvice, you have the option to visit the park on subsequent days on the same entrance ticket. The park hotels are overpriced, but this is one benefit of staying there! Then, if you happen to arrive before dark the first day, you can head right into the park and start checking it out then go back in the next morning without paying again. There's not much to do in or around Plitvice at night, so if you won't be arriving early, I'd probably have an early dinner elsewhere, unless your B&B/Soba offers meals. There is one pizza place in the town at the place that rents ski equipment but not much else in the way of restaurants as I recall.
I'd keep an eye on the weather, too, and if rains are predicted for your planned full day at Plitvice, maybe plan on arriving early that first day and getting into the park on a sunny day if that's an option.