I think it would be enough for events to just say "this is our niche: X type of dancing with Y mix of music with a core audience of Z demographic" and people would just select themselves.
In theory I agree, but tango people are often terrible judges of themselves.
Last night at the milonga, there were (let me count) seven leaders I know of who – via social media, or at the bar when I worked it, or in group conversations – have made it known that they find the floorcraft here atrocious and would prefer to dance at encuentros with a respectful crowd. What were they doing last night when it was
extremely crowded? Cutting across two lanes, staking out three or four metres of space, and taking steps back along the line of dance. Their harem of preferred partners were fine with this . . . and none of those followers would give
me the time of day if I looked toward them for a tanda, even though I dance small and don't back up.
One of those people organizes encuentros. Another is associated with a studio that does. Two more are musicians who offer and play private events. All get invited to the others' events. So do all their favorite followers.
If they said, "Respectful, smooth-flowing tango for mature dancers tired of the chaos at the milonga. You know who you are," well, anybody who actually took them at their word would be shocked. Say, a tourist who doesn't know them at all, saw the advert, and decided to go. It's for the best that they invite one another to their events in private.
We also have a few DJs who go blah-blah-blah about being tired of the ancient standards and promise new discoveries. Then they play strictly simple rhythmic pieces no more recent than the 1930s, better suited to canyengue than to today's tango. One of them organizes stuff, and if he said, "Y mix of music," anyone who believed him would be cheated. Again, it's for the best that he invites his friends who think some OTV plodder is a "new discovery."
In the balance, "invitation only" is for the best. It's just that using "level" as the apology for not giving out an invitation is a garbage excuse. Being honest and saying, "My chums only," would create a whole lot less tension in the community.