We use XenTag for this. This makes the best content easier to find, adds significant pagerank to old threads, and helps categorize the threads as well. It also creates a very organic way for members to discover the best threads.
For example, in addition to your other tags on the thread, you could have a tag for "most liked threads," "most viewed threads in 2014," etc. The more tags you add, the more PageRank will be brought to the threads and the more helpful links will be added for people browsing for content.