We did the tourist track of Arenal/Alajuela/Poas and then also spent a few days on the "road less traveled" but at no point did I really feel unsafe. Sure, it's not always 8-lane highways, but roads are more than decent and considering the immense natural beauty and wildlife, it felt wrong to even expect highways to be there.
I happily tell folks that Costa Rica was one of my favorite countries to visit (and make sure you keep sipping on Fresca and their incredible coffee while you are there!). To each his own I guess.
Edit: Another Pro tip we used: Used Waze instead of GMaps. It's incredibly popular in CR [1] and we felt it had much better directions compared to Google Maps across the country, especially wrt smaller bylanes.
[1]: https://www.washingtonpost.com/news/innovations/wp/2014/10/2...