Might I suggest another way of approaching the site. First and foremost, the "Newest Posts" area is the most powerful function for obtaining the latest things going on. This shows ALL posts which have received some sort of update. This helps you keep in touch with any new happenings on the board, including any threads you may have alerts for. Until you physically check the thread, it will continue to show up in the newest posts area. Once you've skimmed through this area and you've checked everything that looks interesting, you simply dismiss all the rest of them by clicking "Mark Posts Read". This will get rid of all the notifications for the entire board, unless you're clicking it from inside a specific section such as "N54". In this case it will only dismiss the new post notifications for that particular section.
Also, notice the "History" link. Clicking this will show you a history of all the threads you have visited recently. And lastly, although it is currently hidden, there is a watched threads area. You can find it in your profile area on the left or by clicking this link:
https://bmw.spoolstreet.com/watched/threads
When you reply to a thread you automatically start watching a thread. You will get an email notification for the FIRST followup response to that thread only, and will not receive any more email notices until that thread has been checked. You may also click "Watch Thread" in the top right corner of a page to manually subscribe to that thread without replying to it.