These "invisible" shows aren't even for sale at the box office - correct?  Didn't someone call them an "artist-only" sale - or something like that?   I just assumed that these on-sales are for fan clubs, band mailing lists, etc.   It's a way to make these tickets available to those groups without requiring a password.  Not a perfect method, obviously, but probably fairly effective.
I don't think it's accurate to compare these to soft sales.  Soft sales are meant for the general public - they're just not widely advertised.  These "invisible" shows are specifically hidden and not meant to be available to everyone - including boardies.  The fact that you can find them via a web search seems to be poor web design, more than anything else.  I wouldn't be surprised to see that disappear in the future - especially if the links are consistently made public knowledge.
As for this thread, I don't see much of a difference between posting these links here and other people posting our presale passwords to other forums.   I think it would be better to post a note saying the tickets are available, then share the links via PMs.   Soft sale shows are fair game.  They're listed on TicketFly and available at the club, so post away.     
I think we've got a nice little loophole in the system here.    The more it's advertised, the less effective it will be.