I’ll be taking the ferry from Korcula to Split at the end of June, and am wondering if spending a few hours in Hvar on the way would be worthwhile. Basically, 10:30am until 2pm so just a wander through town and lunch. It’s certainly easy enough, negatives would be crowds, heat, and possible midday siesta closures. Is Hvar so different from Korcula and Dubrovnik that I should make time for it? I’m buying ferry tickets beforehand.
Hvar Town is different than Korcula Town and Dubrovnik, both of which are walled cites. I haven't been to any of these places in June, but I'd guess all of them will be mobbed with tourists anyway. What will you be doing with more time in Split instead? There's an easy hike up (20 min each way?) above the town with gorgeous views down on the town and the water. That to me was probably the highlight of my day trip there. If you have 3.5 hours that's barely enough to stow your luggage, have a quick lunch, and do the hike and back (since you need to be back at the catamaran in time to get on, not just arrive as it leaves. There are a lot of catamarans back to Split, so unless you have some need to be in Split at a certain time, you could stay later.
I'd guess it will not be cheap to stow your luggage while you are visiting.