That's the way most online forums are.  Rarely do you see users who maintain a high level of involvement year after year after year; either they tire of the forum or of whatever hobby that forum is supporting.  This is hardly the fault of signature campaigns.

I would say my opinion is biased as well, since I participate in a sig campaign, but it's no more biased that those who don't participate and don't like it.  I actually see more spammy posts/posts that make no sense/bad google translation posts from people without ad signatures than those with.

Support the little guy, both advertiser and avertisee, keep paid signature campaigns around.