Trip to Croatia, need your expert advice :) (Zagreb)

Hello lovely Croatians, I'm planning to visit Croatia end of coming May for 6 days, and I need your advice on the cities and towns I should visit. I'm already planning to stay 2 days in Zagreb and 2 in Dubrovnik. But will still have 2 days left to fill.
Can you recommend towns to see during the remaining 2 days, apart from Split and the Plitvice Lakes, because I'm not totally convinced about visiting them :)
Thank you