Crazy CR plan?
 

Arenal 1 night, 2 nights Monteverde, ??, 3 nights Dominical, back to SJO? What to do, where to go in the middle? Thought about Montezuma, but ferry seems like too much having to be somewhere at a certain time. North to Liberia and a playa on the west? Help or suggestions?

I would never do this - way too much traveling and not enough time to enjoy things. You can easily spend 3 or 4 nights in Arenal alone. We spent 3 nights in Monteverde. When we went to the beach, we spent 4 days there. I think you need to focus on what you want to see and do most and then narrow it down.

How many nights total is your trip? Right now you are going to be spending a lot of your time seeing the road with your plan! I would definitely add more nights onto Arenal - there are lots of activities there, enough for 3 or 4 nights. You will spend 1/2 day getting from there to Monteverde.

At Arenal you can hike the hanging bridges, do the Cano Negro wildlife refuge trip, visit thermal springs, hike or horseback in the national park or do a zipline/canopy tour. Most people spend at least two nights here or longer.

ARenal because I'm a volcano geek (absolutely no interest in zipping), but it might be obscured due to rain anyway; the wildlife/hiking in Monteverde, and then 3 days before Dominical. We pack a lot into a short time whenever possible, and "seeing the road" is often a favorite part of the trip. So, any suggestions besides more time in Arenal? Beach?

Have you been to Manuel Antonio? It has a very pretty beach inside the park, really easy access to wildlife, and lots of restaurant choices. It's a good choice if you want beach access. If you're a volcano freak, you might be interested in seeing Poas.

Or the two volcanoes east of San Jose, Irazu and Turrialba (beginning or end of trip).

Or the two beautiful volcanoes in Guanacaste--Miravalles and Tenorio.

From Arenal, you can do a daytrip to the Rio Celeste and hike Tenorio. Beautiful river, nice hiking. 1/2 day.

You've got good beach time already planned at Dominical. There is so much more to do near Arenal than ziplines. I can't imagine just being there one night.

Even though you said other than Arenal, still recommend more time in Arenal! There's a ton to see and do in the area. MUCH more than zip-lining!