I have cobbled together a solution. It doesn't really save the entire thread, so not sure if this is useful for your needs:
1. Change your forum settings to view maximum number of posts per thread
2. Change to mobile view (I find it easier to read)
3. Download Stylebot and Singlefile Chrome extensions
4. Use Stylebot to change font sizes, padding settings, hide unnecessary icons etc. as needed
5. Whenever you want to save a thread for offline viewing, hit the Singlefile/Process icon in Chrome. This will save the htm file locally
Like you, I'd really like to be able to save an entire thread but also block certain users (i.e., all the users who contribute to threads with boilerplate insights like "SEO is a important aspect of IM. A key part of SEO is building quality backlinks. Thankyou."