Your realistic choices for Nicaragua would be San Juan del Sur, a beach town just over the border, or Granada, a wonderful colonial city about 90 minutes from the border. If you were staying at Playa Hermosa, a good choice not too far from the airport for your flight out, that's a good 1:45 to the border. And who knows what the wait will be at the border Christmas weekend? My concern is that you'd have so little time in Granada itself. I also see that Costa Rica Shuttle charges $300 one way to make that trip. Yikes. The whole thing doesn't seem worth it for one day to me.
I think Nicaragua deserves its own trip. I'd plan that for another time.
Santa Rosa National Park doesn't have that much infrastructure. Rincón de la Vieja NP does. There are lots of things to do in the park. There are also a couple of lodges within the park, and you wouldn't be far from the airport the day you fly home.