Casual fans don't come to see Dax/Sacha, but personally, I think between Dax, Sacha, Henry, Petke, and now Marsch the only time RBNY generate news that the casual fan will see, its always negative stuff. We rarely create any positive buzz for the team. None of our transfers are ever noteworthy, besides when a friend asked me who Kaku was because we spent some coin on him. And since the team doesn't believe in ads, creating buzz is the only way to stay in the casual fan's mind so they go to a game.
BWP getting to 100 goals is good buzz, but milestones don't happen frequently enough to rely on them.
I guess more positive news/developments wouldn't hurt, but I just think you're overrating the impact of buzz and perception on casuals attending. We are obviously not casual fans, so we tend to think about these details a lot more than someone with no rooting interest would. Out of the names/news you mentioned, Henry would definitely moved the dial for a lot of people; the others wouldn't in my opinion, not for anyone who wasn't already specifically following or at least checking out MLS to an extent. Again, stuff like this might possibly bring an extra 20/50/100 casuals, but it's not the main reason there are 10k empty seats.
As a comparison, I'll watch pretty much any sport if it's on TV, and now live on the 7 line, so I can easily go to Citi Field in half an hour but am not interested enough to have actually done it. If the Mets signed Bryce Harper, I'd probably go check him out this season. Whether the Mets lose 25-1 to the Nationals or beat them by the same score or if De Grom pitched a perfect game or someone on the team got his 3000th hit or 500th homer (arbitrary examples that I think are similar to the buzz you're citing for NYRB) would definitely have zero impact on me personally going to a Mets game in the foreseeable future.
The fireworks night did seem to have a noticeable impact on attendance at RB Arena, so maybe they should do that more often. Not every week as the novelty would wear off, but maybe 3-4 times a year, not once.