I guess it is invaluable but I would still prefer the traditional way of showing gratitude though not in a spammy way. However, I guess in a platform that accommodates thousands, plugins like that are important.
For me personally,i really like it when my post is appriciated by someone setting out time to reply the message and not just ignoring the post.I do also give out a reply to any post i found intresting.This shows that one is been appriciated in a forum.That is something very good plus it will help reduce the amount of time beofre you can posst anything else, plus it is good because it a means of passing information or salutation greeting to someone, it will help in know ing that there are people that saw your posted and liked it