Yes, learning new content with the language is key. Laddering is a term used when you are learning a new 3rd language through your 2nd language. For example, learning French through French for Spanish speakers-type material.
The 80/90% comprehension ballpark figure was more about how much you can understand without looking it up. For example, when I watch a reality TV show like Gran Hermano (Big Brother reality TV series) where there is a lot of regional accents, rapid-fire repartee, idioms, street talk, I can struggle to figure out what was just said. The same goes for a standup comedy show in Spanish with the cultural contexts, inside jokes. On the opposite end of comprehension would be an evening news program where everything is said in a structured manner and the diction is as close to neutral/perfect for the greater region of the news broadcast.
Additionally, the environment matters. A crowded noisy bar can rapidly beat up your confidence of being able to communicate. The Foreign Service foreign language ability scales do account for this.