After several weekend jaunts i can say with certainty that you can meet some interesting people in hostels. Between nights in Monteverde, San Jose, and La Fortuna I have meet people of different ages, from different countries, traveling through Costa Rica for different reasons.
There was the 30 something Dutch guy who now lives in Israel working for a company as a researcher on bats and echolocation. He was in Costa Rica for a work conference and decided to stick around for a few days after the conference ended to see more than just the posh resort that hosted the conference.
The Barcelonans the same night who we met but didn´t see much of as they stayed out late partying.
The Canadian woman traveling with the Colombian woman down to Colombia. They were teachers, the Colombian came up and worked at a school in Canada for a year, on summer break they traveled south together to tour Central America rather than the Colombian flying home and the Canadian doing whatever Canadians do for fun in Canada when not working.
The French woman traveling alone who wanted to know if I thought she should go ziplining even though she wasn´t there with a group. I said most definetely. We also ended up talking about Costa Rica´s international image versus reality.
The German girl in San Jose passing the night before flying home to Germany the next day. She and her roommate were spending there school vacation traveling around Costa Rica. We actually ended up talking about the military in Germany versus the US and about Syria.
Four Spanish girls traveling together after finishing university. We were the only people in the hostel and spent about three hours playing cards with the hostel manager. Got lots of Spanish practice in that night!
And these only cover the people I talked to for a while not the people I met in passing. It also is onlly people I met in hostels, none of the people I have met on buses or on tours as I have traveled the country.