No, that's not completely true. An IP has no value if people are not willing to pay you for it. Public goodwill, name brand recognition, and the like all have value, though they are harder to measure.
True, although my understanding (admittedly based more on Anglo-Australian than US trademark law) is that goodwill cannot be assigned without assigning other business assets.
I know that you are responding to a point about the GSL but your comment about "unlimited" seems to imply a conflation of the two licenses and the OGL is the license most of us would want, not the GSL
My comment was about trademark licences - I referred to "a royalty-free trademark licence of unlimited duration" - so I'm not sure why you think I'm talking about the OGL. The OGL is a copyright licence, not a trademark licence.
rules are never truly off limits to anyone nor are they able to be trademarked.
I think you mean "rules cannot be copyrighted". Rules absolutely can be trademarked, in the sense that WotC absolutely can sell rulebooks under the trademark "Dungeons & Dragons" and if you attempt to sell RPG rules under the same trademark you will be legally liable to WotC.
Rules, as such, have no real legal protection (which is part of the reason there are so many Monopoly clones), though the copyrighted presentation of them might. What the OGL does, and does well, is make rules and the application of those rules, open and available in a way that allows other companies to expand upon them freely, without having to worry about the finer points of treading the line of violating copyright.
From WotC's point of view, here are two options: (i) release text in which WotC owns the copyright so that other can use it for free; (ii) publish my rules, maintain control over my copyright text, and let others do the work of reproducing my rules without violating my copyrights.
I would think that option (ii) looks more attractive, especially given that I probably don't
want other publishers publishing my rules, as opposed to publishing material to be used by those who have bought my rules from me.
publishers are free (indeed obligated under section 8 of the OGL) to delineate which parts of a book are Closed and which are Open.
A publisher who attempts to "close" material which is OGC - whether OGC in virtue of a declaration of such, or OGC in virtue of being derivative of other OGC - is in violation of the license, and perhaps also in violation of other people's IP rights.
Companies can actually publish compatible game material without it, but its simply, imo, going to be a little more of a headache (Judges Guild used to do it for AD&D for instance without a license).
Sure. But if you are suggesting that Paizo could publish PF in its current form without a licence from WotC then I think you're badly mitaken.