I like both of this ideas. I think they are a good start.
1. To attain ranks above Member, you'd have to earn some number of merit points. Merit points would be awarded in a monthly vote on best posts of the previous month, with various measures (TBD) to prevent gaming of the vote. Winning merit points might also come with a BTC prize.
How do you plan to conduct the voting? Forum members ranked "Member" probably number in the thousand now. Are you planning to add an Upvote feature for posts and use the results to determine who ranks up? That might be prone to Like farming like what is happening in Youtube and FB.
As for the BTC prize, I'd rather not have money involved here.
2. Create or designate some sections as "serious discussion" sections, with no signatures. In those sections or maybe in different ones, also have poster restrictions such as Member rank or above only. And/or allow topic-creators to set these restrictions on their topics, similar to selfmod topics.
I'd go along with the topic-creators modding their own threads.
Okay here are a couple of ideas that I could think of:
1. Start banning users that post 5+ posts a day that can be termed as spam.
2. Require unique phone number authentication for every user.
Hmm, with #1 there must be a criteria on what would constitute a spam post and people should be able to vote on it and then the mods can review the ban request first. I mean, I've seen users who have beef with each that start having arguments whenever they meet in a thread so it's not unlikely they'll keep downvoting each other.
#2 might make some uncomfortable but I'm personally fine with it. There are exchanges that require it anyway. I also like that it might protect users against hacking if the authentication is required every log-in.