To me, if you want an investment- buy land, or stocks. Hobbies are not, and likely won't ever be, an investment. Granted there is time invested, money spent. But no sure returns.
I am a relative newcomer to this hobby, so I cannot speak to values. But watching other "sure-bet" collectibles-they all wax and wane. And listening to other collectors, prices are down(though they sure don't seem that way to me!).
But, I think tolling the death knell might be a bit pre-emptive.
I think, if you do want the hobby to thrive, the key is promotion. Not at tractor and steam shows(those folks already have exposure) but at schools, churches...anywhere kids are.