That's the problem though, isn't it, particuarly the Spam thread is like an emoticon invasion.
Making a Spam thread a classic (one, I might add, that was actually made of Spam split off of another thread) means that people on this board will think 'oooh, it's ok to post Spam, in fact, it might even end up featured!'.
It's not simply a question of how many replies there are, but also how many different people were involved with the thread, yes, the Spam thread is very long, but how many different users were actually posting in it, and how many posts did they make per user?
Edit : Flicking through the Spam thread, if the posts by Snail, Jr2 and Mobius were edited out, the thread would be a fraction of it's current size.