The "watched topics" I've never looked at but just did now. This could solve the problem quite well. Another option is to use notepad, Word or something similar and copy the web addy for the particular thread you'd like to save:
Example - This includes a description of the topic at the end as well.
http://www.steelsoldiers.com/index.php?name=PNphpBB2&file=viewtopic&p=104438 (Saving favorite thread)
http://www.steelsoldiers.com/index.php?name=PNphpBB2&file=viewtopic&p=104438(What is this generator motor)
You can then email the file to hotmail, yahoo, gmail, etc. so that you'll always have a copy of it. If updates are needed, just re-email the updated file. You could also eliminate the need for a Word file or similar by just creating an email on one of those online email services and just forward the email back to yourself with the updated files you'd like to recall. You'll always have that email to refer to.
With all that said, though, the "watched topics" seems to accomplish the task just fine too.