Flew with them last year IAD-PTY-SCL and back, and was able to choose exit row seats at time of booking. I don't have any kind of status, and the tickets were deep discount economy.

They do take the Spanish-speaking thing seriously - luckily my Spanish is decent, but my friend unwittingly responded "no" to the question about whether he spoke Spanish, and they promptly moved him to a middle seat near the back of the plane!

I think Copa has a bid-to-upgrade scheme, but doubt you'd luck into a free upgrade unless you're a Copa elite.