For example a Junior Member needs 10 merit points to become a Member while a Sr.Member needs 500 merits to rank up, I think it should be the opposite, if the aim of the merit system is to lemit the number of spammers then a new registered member should provide more effort to prove himself.
If he succeeds to collect a high number of merit and ranks up, that means he is not a spammer and ranking up should become easier.
What do you think?
What do you mean the opposite? You mean you need something like 500 merit to become a Junior? I think there should be a merit requirement for them as well as their signature being removed, but it shouldn't be unnecessarily high. They will already struggle to get something like ten merits, but a decent poster won't have much issue with that whilst it will also severely curb the worst of the worst posters and also bots etc.
Self-moderated thread extension.
Self-moderation is great but I want to propose an extension to it. Allow the OP to choose who can participate in their thread, E.g if I want to create a discussion thread, Instead of self-moderating it, I would just choose the ranks who can respond to it. It's not a tool to counter spam but it could help in sub-boards like "Bitcoin-Discussion" and "Offtopic".
That has literally been suggested, along with being able to prohibit certain users from posting in it so you don't need to waste time removing the posts of users you don't even want posting in there or breaking your 'local' rule etc.