I got tired of not noticing that I was reading old threads from the beginning when they get resurrected by a new post, and wrote a Chrome extension. All it does is change the background color to lavender on any post that is more than a year old.
Let me know if you want to try it out and I might eventually write some docs and figure out how to publish it. For the moment, you can check out the code and load it as an unpacked extension: https://github.com/wsmoak/coth-forum-ext
