There should be a system inside the merit points store for each world that lets you spend your extra merit points. It probably should be a single buff that affects that world or your family, and only pops up after you spend all the needed merit points in that world so that you aren't spending merits on the bonus buff possibly stunting your progression.
#Extra Merit Points Store (EMPS)
urban tree
urban tree
Obviously this is pretty vague because I want to hear other players take on this subject, primarily since I dont really know what should be for each world, I understand it would push end game players farther up the ladder but tbh they earned it if they got all merits for each world.
drifting thistle
Id be happy if you could get some visuals out of this