True about first impressions. But note you do get to use #newhere
again if you so choose. Maybe you're back from hiatus, or it's time for a welcome-wagon post of encouragement or something.
While your posts will always be in the timeline of those you've chosen to share with, everyone else will only see them according to the tags they follow. I conclude from that that it's not spammy to post on any topic (niche or mainstream) if you have something�to say, as long as the tags you use are relevant. Without any mysterious central Algorithm shaping each user's personal feed, post tagging and followed tags are the name of the game.
I'd kind of like to have "groups" as a feature too, but no complaints.