It seems that now it is not a good time for start again this signature campaign, maybe it will be better to not "reopen" it anymore.The fault is that a lot of users have been banned in these days, due to their spammy posts and I think the all signature campaigns are dying slowly.
You may be right about banning spammy users (this is a good thing, IMO). However, I don't think that signature ad campaigns will disappear forever. As long as folks are opening new btc related ventures there are going to be people looking for ways to advertize those ventures. From what I can tell, signature advertising has been really useful for businesses to get their names out there.
You may also be right that Primedice doesn't have a lot to gain at the moment from a new campaign as they already are well known and have huge amount of the dice market share (as far as I can tell). I would think that signature advertising is going to be especially useful for startups and new companies that are trying to get folks to try them out. For PD, they've got a quality product that's already known so they may not really need this as much as a new kid on the block.
I think that conditions and rates will continue to change in response to a number of variables but I don't think that signature ad campaigns are going away anytime soon---they've just been proven to be too useful for advertizers.