I thought about doing that recently, and perhaps I should. I haven't seen a merit giveaway thread in a long, long time, and the last one was by actmyname if I'm not mistaken. The only issue I have is that the members who post in them don't read the requirements, don't understand that I wouldn't just be giving merit away for shitposts, and that if I created such a thread it would just die off like the other ones have. I suppose I could keep bumping it, but I think I've made the offer enough times that anyone who thinks their posts would hold up to my standards would have PMed me by now.
But I'll consider it.
You are already merit showering the users who have good post quality and came into your eyes and i am one of them and still you have the generous offer of PM which members can avail to have a post history check and if you find it suitable you are generous enough to merit them upto the limit of 50 in a month.Like recently you merit shower @Mpamegbu, @icopress,@showoff and some others also which is quite good.
Opening a merit giveaway thread will have certain limitations like you said bumping them as members don't take full advantage of such threads and keep on repeating and making threads like how to earn merits and all that.But still you could open a thread for helping users to achieve certain ranks like of @Ratimov but for me your current merit criteria sounds better.