First, here (tel aviv) the basic wework costs range from $150 to $600 depending on location and frills (eg private office). This sounds like pretty standard pp office costs. They tend to be well liked by the people who work there. Well kept, well located, social, etc. Unless paying money for office workspace is ipso facto a luxury good, this seems like a regular good. Money for services at market rates.
Second, people working there range. There are some are "startups" without definitional grey areas but these're just some of the tenants. There are external employees of regular companies. All the work from home people that prefer a shared office, at least part of the time. Apartments and cafes are still active, but it turned out there's room in the market.
The way I see this is (1) internet has created more demand for flexible offices. (2) The older versions of this were pretty crappy, so these guys moved in.
As to wework as an investment... IDK. But, you could say that about a lot of companies. As a company offering a product to a market for a price, seems like a fine company. The product is sensible. People like it. It will vary geographically, but seems perfectly plausible that wework-like offices will grow to house 1m workers.