honestly, i quite like both the ideas you've come up with;
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.
while the prize would give a nice incentive for post quality, i can't really picture in my head how this would work out in practice. assuming the voting would be done manually by actual people, and since merit points would have to be awarded for a large number of users (maybe the entire userbase?), id like to think some automated system would work better, with select individuals running quality checks every now and then. maybe even implement an increasing penalty to merit points for spam / off topic posts (with a 'cooldown' to reset the incremental penalties), with a temporary removal of signature privileges if they have their points go negative. not really worded that well, but just some rambling thoughts on the idea. if you could elaborate a bit how you plan to actually implement this merit points idea i'd appreciate it.
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 wholeheartedly agree to the idea of having a 'disable signatures' idea for thread starters; it'd be a simple fix for people who want an actual discussion that would eliminate a lot of spammers. however, i feel these threads would be 'covered up' really quickly by threads that allow signatures, just from the fewer number of users that would post in those threads, and would just die out real quick. a 'serious discussion' section though, would eliminate this issue, although im not sure how many people would frequent those sections enough. in addition, how many of these sections would have to be created? maybe one for every main topic as seen on the index page (one for bitcoin serious discussions, one for mining, one for marketplace, etc), but wouldn't want to flood the forum with sections that may or may not be 'dead.'
just some rambling thoughts on the ideas you've presented, but ill try to think up of some well thought out ideas in the next few days and post them here later.
also, any consideration for an account related issues section (bans, locked / hacked accounts) in meta? it seems those threads have been flooding meta quite a bit lately.