The thing is--and I'm not saying you specifically--but worrying about a place losing "its historical roots and what makes it that special idyllic mountain town in the first place" inevitably has to go hand in hand with strong NIMBY policies. Which isn't even "wrong" in any absolute sense whatever the growth at all costs crowd here may want.
Though, really, not even that helps because towns can't actually (or really want to in general) arbitrarily prevent outsiders from moving in. So a desirable location just ends up with a different group of people with the money to purchase existing housing.
The way I look at it is that every popular community does have to make decisions about what is / isn't going to be part of its yard (front or back), but that optimizing for either economic accessibility or quality of life can be hard, and going for both is considerably harder. Good policy is difficult (and rarely aligns with either simple economic ideology or social aesthetics).
That said, I can't help but wonder if it is possible to shape how people buy. For example, with the existing very limited housing stock being exacerbated with large capital chasing it, I'm inclined to think that there should be property taxes that are a function of housing one already owns in a given market and supply on the market. So... want to buy a new house and keep your old one to rent out? Want to buy a third in a market where there isn't two weeks of supply on the market? Maybe you'll pay a bit more, both on the transactions and yearly. Want to buy your twelfth or twentieth unit as part of a fund or trust in a market where there isn't a week of supply on the market? Maybe you're going to get hit hard, and you should try to find some other productive use for your capital.
A lot of these people are really only moving into the interior mountain towns because places like coastal California where the economic activity is that allows them to pile up this kind of wealth has become prohibitively expensive due to their own NIMBY regimes.
Metro California problems follow metro California popularity/growth.
Policies you're calling "NIMBY" are rarely the underlying cause. They're reactions. Some of them exacerbate certain problems, some of them attenuate others, but not the underlying cause.
NIMBY is just a symptom of the problem... The problem is development, wealth and consumption at all cost.
If people lived in normal houses, had normal job and lived normal lives where they didn't have to escape to feel normal, then we wouldn't seek out mountain towns as places to live, but rather places to explore.
Instead, we amass sheer amounts of wealth, property, exclusivity, we build so much of our society around celebrity and uniqueness and feeling special. We value huge houses with lots of rooms we'll probably never use and as long as "we win" - we don't care the cost.
Here in Austin - we're seeing the result of people leaving other cities. They look here and go "wow its cheap" but the people who have lived here - and lived here for EONS are going "wow, its getting expensive".
If you bought a house on fixed income and paid it off and worked a full life - we're getting to the point where your dream is no longer a dream. Sure, the house may have equity but its a tax liability - so you have to move..
Where do you move too that isn't being impacted? Where do you go to survive on fixed income and just live?
Is it NIMBY when you just want what you worked an entire life for or is it really something else?
There have always been people who wanted to live in remote mountain/beach towns. Ski/surf bums are not new. What is new is being able to work remotely through the Internet for a company located in some place where there is more economic activity or being able to pile up enough wealth in places like coastal California to move to a remote area and semi-retire at a youngish age.
If you're retired on a fixed income in Austin and own a house you can defer paying property taxes until you die so there's no reason this person should have to move.
Though, really, not even that helps because towns can't actually (or really want to in general) arbitrarily prevent outsiders from moving in. So a desirable location just ends up with a different group of people with the money to purchase existing housing.