Just because there are some number of people, somewhere in the world, playing a format does not mean it's 'healthy'. Is Alice (alliances-ice age) sealed a healthy format? A year ago a few friends ran an 8 man tournament with some old sealed product they bought of that format, so therefore it's still an alive and kicking format according to your logic.
There is like one vintage tournament a year that is on the scale of the standard tournaments being hosted EVERY weekend.
There's well over 50,000 standard players for every one vintage player. There are probably at least 1,000 legacy players for every vintage player.
Vintage is a dead format, with a few pocket niche areas in the world that can reliably put together a weekly FNM level tournament for it.
The prices of vintage cards continue to rise due to scarcity and their collectible status. Vintage tournament results do not make vintage cards rise/fall like they do in legacy/modern/standard because the scarcity is the main factor in their rising prices. As long as magic continues to grow, the cards that are the rarest will continue to go up in price overall, regardless of the 'health' of the formats.
There was about 5-6 guys in my area that could put together any vintage deck they wanted a few years ago. Almost all of them have since sold off their power and simply play legacy events instead now. Their reasoning being 'no one playing vintage'. Granted, that's just my area, but since you keep using the fact that your area runs a weekly vintage tournament as evidence that the format is healthy, I think it's just as relevant.
Yes, someone will still play vintage and legacy no matter what. In 40 years, Magic could be completely dead, WotC out of business and not making new cards, and there will still be a gaming group that keeps their old cards and plays kitchen top vintage among themselves. It will not mean Magic is still alive and kicking.
Legacy's prices will continue to rise as long as magic's player base continues to grow. No matter how expensive the format, there will be some number of magic players with enough disposable income and patience to acquire the cards. How many people play it, and how many supported tournaments are able to be run will determine how 'healthy' the format is. If the cost becomes close to vintage prices, making the barrier to entry too high for most players, there will be less and less legacy tournaments. The prices will taper off and remain stagnant instead.