I am not personally in favor of closed discussions - if I want that I would direct message or e-mail communication or create the same type of group on skype or some such thing.
I like the forum for airing ideas/discussing things of a wider nature - of general interest - or where a large funnel needs to be cast to gather the knowledge (and intelligence) of people (regardless of their monetary nature or success in the business). Those with pre-established success in the business will be the most tight-lipped - so they are not the people I would want to address or expect anything from them (since most exchanges with them will always be in terms of money or “what can you do for me” - though all social relationships are more or less of that nature - with the vip member types it is more blatant).
I have some experience with forum dynamics in an unrelated field (i.e. from participating etc.) - and general sense there was that a closed forum RAPIDLY loses it’s “dynamism” or vitality - as it winds up being populated by a few - and the power of a forum is EXACTLY that of REACH - i.e. there maybe a junior developer in Korea who has an excellent response.
However a VIP area maybe valid for members here who wish to exchange ideas for $300 - that type of thing - perhaps a specific incarnation for that may be for example when mrkisss or affliate or some of those sell their idea for $500 - they may actually want THAT sub-group to have a place to talk - so creation of THREADS which are hidden may have some value for that.
The negative of such sub-areas within a forum is that it creates a sense of “what are people talking about here” (as “those in the know” will be talking some other language) - and this will hurt the “open” nature that people expect of such forums - precisely the reason people are willing to share some ideas (which may in some instances be worth money as well) - is because they now they have gotten similar help without strings attached in the past - so that creates a warm feeling for such forums. Once a forum starts experimenting with sub-forums that are “exclusive” - that will begin to harm the “niceness” factor - with a result that you will get less open participation.
Given the needs expressed for such a VIP forum - does it have to operate as a sub-forum of this forum ? Or could it be a completely different forum/website (better to not harm the environment of this forum) ? The value of having an “joint” forum - maybe that “VIP members” from one forum can express their superiority on the “plebes” in the open forum - however I am not exactly sure how that will be received - I suspect that type of dynamic would suit an possibly accomplish a mission where the VIP forum is the MAIN forum - and the supposedly open forum is just the “funnel” to get people to become paid members. Again this completely changes the nature of the forum - to essentially a paid forum. So it could be argued that the actual rationale for a VIP forum seems less to cater to the “special” needs of the super-rich - than to create an environment for a paid forum.
I do not have experience with such private forums - so the example cited i.e. marketing forums etc. - may have merit (I don’t have a sense for that).
But one advantage I can see for a private forum is that it would keep the discussion out of reach of Google search - which could be valuable (but would also remove much discussion from getting an audience - as some of the participants/new blood on this forum may have arrived precisely via Google search for issues that were being discussed “in the open” on this forum).
So in conclusion - my own sense is that making a forum “private” immediately reduces it’s visibility and vitality. If the purpose is to have “profitable” developers only discuss between themselves - then what is to prevent further subdivision between them - for the uber-profitable wanting a super-profitable group. You can see this is very similar to how Scientology works.
Worse - the VIP nature of a closed forum - may give some a false sense of privacy - when there is really none (all discussion will be archived).
The forum moderator also has to accept the responsibility of hosting such a closed forum - where discussions will more readily turn towards a “black hat” nature - i.e. legal and illegal means of manipulating Google etc. will be discussed.