but the fact that someone can go from 0 to 1800 "friends" in a week (assuming they are a noone like me) has to imply the lack of value of an account with that many friends (and IMNSHO the "service" itself).
"followers" - not "friends." And not necessarily - think about supply and demand. There are a limited number of twitter accounts. If you happen to have a good twitter account name, it may attract many followers and be of value.
Plus, it isn't easy to get that many followers. You can't just sign up and make it happen. I think the number of followers would be of value from at least an advertising perspective.
Why do you assume someone with 1800 followers is a nobody? I'd guess they have a blog that is read by a decent number of people or something like that.