I think the forum's Webmaster has a lot more insight on this than any individual person using parts of this forum, assuming he tracks some key analytics and is willing to share them with you (you can contact him directly). He's the only one who can possibly see and monitor "the big picture" more systematically than others. Some key data might include: distribution of participants based on the number of postings (that will tell you how many people likely fall into "newbies", "regulars", and "heavy duty" participants); top keywords used in postings; number of threads by country or topic (there are standardized drop-downs so this shouldn't be hard to sum up and measure historically). All of these will have all sorts of caveats due to repetition and similarity in questions, and inability to segregate truly unique, unduplicative threads and more definitional issues than I can count. If you're undertaking a research project on this, you have to know something about the group you're studying first and what their characteristics are between one travel forum and another. Probably the most relevant to you is how many and what kinds of threads are deleted by the Webmaster due to either rhetoric or failure to adhere to the community standards (these two things likely overlap, but it really depends on your exact definition of "rhetoric").
This is purely anecdotal (and hence limited) but the only trend I've noticed that differs from the typical is an uptick of posters either concerned and/or asking for validation to travel after news of a terrorist attack, whether in Turkey, France, Belgium, etc. There have been many animated discussions about perceptions of "safety" that receive more responses than other threads, mostly because someone will post a political slant which prompts other comments or rebuttals.