Even now there are members who do not wear paid signature or avatar and they post as much as those who are in signature campaigns. But I think if signature campaigns are removed, there will a lot less activity on the forum, I doubt if users who are making 20 posts or more everyday will still continue to do the same. The discussions on the forum will decline to something like Altcointalks.

I don’t believe signature campaigns are a major reason for spam in the forum, many campaign managers do not consider such posts eligible for payment, if anything signature campaigns have increased the quality of posting on the forum. Before the bloom of signature campaigns, the forum was a spam fest, the merit system was introduced to make it difficult for spammers to rank up, with this system in place members had to improve their post quality or remain in the same rank with airdropped merits. Campaign managers understand this too well, that’s why they make it a requirement for participants to have a certain amount of amount earned in 120 days before you can apply for sig campaigns.

Yes there will be no need for alt accounts because there will be monetary benefit to creating one. Account farmers would run out of business because people will not be interested in buying high rank bitcointalk accounts anymore. No signature campaign on the forum will definitely kill account farming, buying and selling of accounts.