I think the style and genre of the intended game using alignment necessarily influence interpretations of alignment in that game and vice versa.
Agreed.
In an action adventure genre with typical "goodish" PCs, they use fairly straighforward tactics including violence to solve their problems, and do so effectively.
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In such a game, A True Neutral(TN) attitude that major change is impossible or detrimental isn't a useful one, it's the attitude of an obstacle NPC or antagonist.
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My personal problem with TN is that I prefer straightforward action adventure, and "don't bother" TN is a poor fit for such a game style.
Also agreed.
The sort of "action adventure" style you describe is one that I would say doesn't really need or use alignment. That may be overly sweeping or simplistic, though - the core of what I mean is that, in an "action adventure" sort of game, the moral answers are already known and available, the goals are clear, and what is at stake is immediate choice of means (is it better to strike now, or to rest first?) and the efficacy of those means.
In that sort of game, it seems to me that the point of labelling the PCs "good" and their enemies "evil" is simply to provide a pretty thin layer of colour, and perhaps to provide some sort of assurance (with both ingame and metagame aspects) that the PCs aren't just being vicious murderers.
In that sort of game, labelling an NPC "true neutral" would indicate, I think, that they are some sort of Yoda-esque mystic or hermit who might have information or other resources the PCs need, but that they will only hand it over under certain quirky or irritating conditions. (I see this as being consistent with your description of such an NPC as an obstacle.)
For naturalistic True Neutrality to play any more significant role in the game - for it to actually become a focus of debate or contention or exploration - I think some sort of set-up like the one I described not far upthread in reply to [MENTION=996]Tony Vargas[/MENTION] would be needed. The play of the game actually needs to put into question whether intentional action and cosmological purposes are merely disruptions to the balance that just muck everything up. That's not going to be
just an action adventure game.
EDIT: I think I missed another theme in your post.
To the extent that True Neutrality in the naturalistic/quietistic mode is mostly reactive rather than active, there is a tension with RPGing, where players have to declare actions for their PCs to make things happen. But I think this tension can be overcome through deft handling of metagame/ingame distinctions: the player is ready to act in order to drive the game, but the PC is played as reacting to particular circumstances that the GM has framed him/her into.
If, over the course of play, the PC succeeds in dealing with the situations that the GM had framed, and re-establishes balance and calm, the game might be seen as having provided some sort of vindication of True Neutrality.
On the other hand, if the course of play drives the PC to become more and more active, and to formulate and implement affirmative agendas, then it looks as if True Neutrality has been refuted in that particular campaign.