Thanks for the informative post. I admit I was just minding my own business posting the way I post when I started noticing the merit statistics by people's profile handles. Now I know where it comes from. Looks like I can just carry on. I'll try to award your post some merit points now that I know I can.
You wont be affected by the Merit system in term of ranking-up, since you have reached the highest rank /for now/. The system is introduced in a way to prevent the abuse of the Activity point system and reduce the spam and shitposting. The merit for legendary members is more for "prestige" /not the right word i know/ or contribution, but you have also the responsibility to distribute the your sMerit points to posts you think they are informative for the community I some way.
Giving merit to shitposts or spam can easily make you a target and you can be reported.
The penalty is negative trust, so you have to be careful what you are doing before sending sMerit to random posts.