This is an interesting point, along with what some have mentioned earlier about low to mid grade books for entry level collectors.
I relate the comic value industry to the housing industry in a few similar ways. Entry level homes will typically always sell as more people look to get into home ownership. And, those that are home owners and want to upgrade have equity built up (and savings I'm sure) to upgrade their house. And looking back to the days where a house was $10,000, those days are long gone. Do I think the housing market can collapse? Sure, its possible, who knows, but people keep doing it anyway because the perceived risk is out-weighed by the expected appreciation. Whether that is inflation, cost of living, supply, demand, whatever. Overtime, house prices have gone up, yes there have been dips, crashes, spikes, that's the risk.
I think comics behave in the same way, history can be an indicator of future success/failure. If someone believes a book to be at a great price, they'll probably snag it. If it's a super-mega-ultra-key, or whatever the cool kids call them these days, I think there will always be a demand for them, enough to offset the risk. It'd probably take a catastrophic economic failure for comic values to plummet, like another great depression. Again, sure, it could happen.
So, back to your point about the insane market. Have we always thought the market was insane along the way, how many ceilings did we burst through over the years? We are dealing with collectibles and collectors, a recipe for record sales over and over, until it collapses. If that happens, yes, it would've been better to have cash-money in the bank, rather than losing X amount in comics.
No risk it, no biscuit?
Jerome