If the administrator forbids or no longer wants any signature campaign here will these merits matter, it's like working in a company you get a better position and pay if you have a lot of feathers in your caps.
Merit will still be matter for quality users because it is like forum member ranks. You received more merits, it is like a recognition of your contribution and value in Bitcointalk community. It is not true for all because earned merit can be easier or harder for different forum members but generally it is one of quality signals.
If I am a good poster, I will make good posts and I am sure I would feel a bit happy when I see someone drops their merit on my posts.
For those who are into true discussion getting a merit is an incentive that they are doing good, but for those who are eyeing to make money through a signature campaign it is a ticket for a seat.
There are good posters who make posts but don't wear any signature and they don't care to join any paid signature campaign. They will not stop posting, sharing idea when all signatures are disabled in Bitcointalk.