I have being doing this exact experiment with Icelandic for ~2 years– I listen to about 1-2 hours of Icelandic talk shows and podcasts a day while commuting, always new material, I never repeat.
Initially, I was chuffed if I could distinguish words (that I didn’t know) from the buzzing noise. Initially only the grammatical particals pop out (definite articles, suffixes on adverbs, etc) One day, I realized that gjaldProta meant bankrupt, which was a word I’d never looked up in a dictionary. More interestingly, I didn’t really understand the news article where I heard the word. I learned hrigja aftur means “call back” on a call in talk show where the caller had a obviously bad connection. There is more context in a stream on noise than you might imagine, after all, the blind learn English largely on input from a stream of noise with no visual context.
There are now 100s of words I’ve heard the point where I recognize them but still don’t know what they mean. However, next time I see the work krof, I will learn it in one repetition because they talk about it all the time on the radio. (It turns out to mean something like central bank reserves)
I used to be able to listen to Icelandic news and read English at the same time. It is getting to the point where I understand enough that it breaks my concentration. When I didn’t understand, it didn’t bother me that they were reviewing a book on knitting.
I think this has helped my pronunciation– I’ve heard a lot of people’s speaking styles. Young girls, academics, men and journalists trying to act serious all have different qualities to their intonation and you can’t learn that from re-listening the same CD over and over.
I’ve a long ways to go, but I think it’s helped. (Listening to foreign language music on the other hand, has never helped me. Dunno why.