What we can do is to have a requirement after creating a new account for users to be able to post links, which means that if someone creates a new account, they shouldn't be able to post links unless they spend a specific amount of time in the forum like 24 hours or something. So if someone joins the forum being interested in the forum itself and plans to stay, they should be okay because they will have the requirement completed within a few days, and those who are doing these things won't be able to post links to promote specific services.
even if it is just a 24-hour restriction it could still deter newbies who actually like to learn or have questions, bitcointalk isn't the only platform where people talk about Bitcoin or other cryptocurrencies. I know the things that you mentioned can be annoying but if the forum wants to attract new people it shouldn't restrict them so much.