Classic sports car requires maintenance and care that is not only time consuming, but sometimes expensive to retain their value. I only recommend this to people who care about cars and do this for a hobby and passion. Some classics will give you insane amount of returns if some weird events strike.
I don't know about classic furniture.
But expensive watches are generally too expensive to begin with. However, the value will stay afloat for crazy amount of time. I understand why people consider them an "investment", however, it will be more like an emotional keepsake rather than investment item that is liquid enough for you to easily sell at desperate times.
Agree on "investing in real estate = destroying the city." But not only city, the economy too. Look at Chinese ghost towns... everybody starts pouring money into real estate that no one lives in, but owns. Value will instantly drop. The stupid argument perpetrated by developer company "world is only getting smaller, and everybody is going to need home" may sound logical but it is wrong. You'd apply for mortgage to "invest", which nobody in 5 years could afford because of the artificially inflated market price. Let alone anybody would rent, because there is just too many supply for the lack of rent-able places.