Of those, the only thing that really merits an update is the poster presentation, and even that is a bit of a stretch. "Submitting" an abstract is nothing, and taking a Spanish class is less than nothing.So far this cycle, I've sent 5 pre-II update letters. All of these letters have been to schools that have sent an email about their admissions process, reminding applicants about the opportunity to submit updates. I have not heard back from any of these schools yet. My updates include poster presentation at a conference (mentioned that the poster was pending review in my primary application), submission of an abstract for poster presentation at a different conference (pending review), and taking a 5-week medical Spanish course for healthcare professionals. Should I continue to send these updates to other schools that accept pre-II updates?
Honestly, update update letters are unlikely to have any impact whatsoever on your application unless it's a truly major accomplishment like a first-author publication in a prominent journal. Keep sending them if it makes you feel better that you are "doing everything possible," but most likely you are just treating your anxiety. The contents of your application prior to the update letter almost certainly is the determining factor in whether or not you're getting interviews.