In this case the PM option can be used if all you wish to do is 'thank' the op. Imo, adding fillers so as just to make the post look less low value is not necessary, especially if all you need to do it appreciate the OP. Rather than writing 2 words using 50, just private message the user.
But merit should be given to high-quality posts and such posts are the exact opposite.
I believe@ranochigo meant the user meriting the original post they were appreciating, and not merits to the seemingly low value (thank you) reply.