To me the theories behind NVC look like tricks to get people to buy into extreme propositions that act as counterweights to flawed biases, approaches, and methods many people in fact have. The theories don't look true and the advice seems merely useful for most people to hear rather than actually true.

Given Sturgeon's law, "merely useful" is pretty high praise.

In any field of endeavor where your goal is to convince someone to change their behavior, it is a given that you must provide a suitable "theory" to be a behavioral mnemonic and/or intuition pump. (Because in order to get a person to act, you must provide them with an intuitive perception that taking (or refraining from) the prescribed actions will produce the result they want.)

It is also a given that most such intuition pumps will contain things that are to some degree, false or wrong, simply because all models are wrong, and convincing models especially so. (Since they have to fit humans' pre-existing biases and cognitive capacities.)

And, if you try to fix that wrongness by being more detailed and more nuanced, you will gradually begin to lose your audience, which for the most part, really doesn't care!

And, even if they do care, they are soon no longer able to grasp the essence of your model, due to the number of bits of information you're expecting them to internalize.

Therefore, a rationalist that wants to obtain useful information needs to have a lower threshold for rejecting source of information based on their epistemic hygiene, and focus only on the predictions made by a model.

For example: the "law of attraction" model is complete and utter bunk.

And yet, if you discard the theory, and examine instead what specific behaviors its advocates say people should engage in, and what specific results they predict will occur, you will in fact find that, well, the prescriptions and predictions are actually kind of right. (See Wiseman's "luck research", which provides far more plausible explanations for how those phenomena actually occur.)

So: the theory is bunk, and yet results are produced... just like candles still burned when everybody still thought "phlogiston" was a thing.

Now, note that I'm not saying that NVC has been empirically verified. I know next to nothing about it other than tidbits I've heard about some of the skills -- and which tidbits I've put to practical use.

What I am saying, however, is that the theories provided by any system of self-improvement, communication, etc. should be taken with a grain of salt, because the practical value of those theories is to provide intuitive understanding and motivation for someone learning to apply the practical knowledge involved.

So, it is these specific, detailed behavioral recommendations and result predictions that should be examined, when examining a practical body of knowledge.

Because, either those behaviors produce the result, or they don't. And if you desire the result, the theory part is completely and utterly irrelevant: all that matters is whether the result is produced or not.

You can, if you wish, always invent a replacement intuition pump -- perhaps even making it so silly that you know you won't be compromised by believing it (see e.g. the Flying Spaghetti Monster), or perhaps carrying out your own groundbreaking scientific research to show why/how the crazy thing under study actually works (like Richard Wiseman).

But if you set your standards for theory so high as to require an academic level of precision, you're automatically cutting yourself off from vast amounts of useful knowledge, and substituting knowledge that usually isn't optimized for actually doing anything.