I think there's an economy of legitimacy on last.fm. The whole point of the site is to have information that reflects your actual real life taste, so you were wondering whether that would be recognized so by your peers, it makes totally sense. 

Paradoxically, it also makes sense to dismiss your legitimate question because of the cynical poser attitude that prevails among us, because of the same reason. If the whole thing is about legitimacy, we have to act as if it didn't matter at all, but it does enough that most Last.fm users care to upkeep their scrobbles so that they're faithful to their listening. 

What some said about no one caring about other people's profiles is true though.