My experience has been totally different here.
We found people to be biased toward being polite. So we found "being excited" was a bad signal for what to build.
The best signals were when people offerred things that actually cost something e.g. reputation (by putting us in touch with important people), money or time (if they're people who valued their time highly).
We still haven't found any crazy level of growth though so maybe it is easy and we're just doing it wrong. Who knows.
It's a short book without fluff, I recommend.
For example: - "This is awesome! I would absolutely use this if it would just have this one extra feature it does not have now." --> I absolutely don't care about this product. Please leave me alone. I have better things to do.
I think OP agrees w/ you and this is their key point -- you can ignore everything they say and just look at how, or whether, they use it. More generally, I think it helps to try very hard to get at the underlying problems people have, and try to make those problems go away. People will use very terrible software (interfaces) if it solves a real problem for them. I think your signals are good generalizations to be clear, I just think we (all of us) regularly gloss over problems by focusing on tech, design, or otherwise "cool" things. It can be really hard to figure out what problems people actually have, and also whether they are significant enough to change their behavior to solve them better.
I have been doing customer discovery professionally for over 10 years as a sales person and PM and there is no 1 method or silver bullet to predict whether the product will be successful.
Talking to acquaintances is terrible, because they are biased (see MOM test). They will tell you all kind of stories, but ultimately what matters is:
Are they going to pay?
Excitement has nothing to do with revenue which in the end is the blood of a business.
To extend this - there is a patter now on Twitter where indie devs are selling to their twitter friends, but is it a viable business beyond that? I don't know.
What I do know is that the only way to validate a product is to get paid and the market will tell you the truth.
Think about it like this. If you show the product to a handful of people that you imagine to be ideal users, and NONE of those people are excited enough about your business to share it with others, then what chance of success do you really have?
To give you a concrete example. I made an app that was a pretty revolutionary take on reading short stories. I had a few friends try it out, all of whom were passionate readers. They said they liked it, but I could see that none of them opened it again after their initial test. To me, that was all the signal I needed to pivot to something else.