This sums it up right here. On top of that the counterfeits only make matters worse.
When I got back into Legos after taking an investment break in 2008, I was watching ebay auctions like a hawk waiting for BIN amount on older sets that I for sure would not lose money on if I bought them and resold them at current market value minus ebay fees and shipping. I was extrememly justified in the high cost as I knew that the prices would not go down.
Well the SSD I bought at a screaming price of 800 MISB back in 1/16 is now worth at best 800-850 sealed now, with many selling sub $800. I lucked out and sold mine at $900 when i felt the tide turning and only lost about $30 after fees and shipping as the buyer lived a couple hours from me keeping shipping low. If they lived in WA I woulda died. I did the same with any significantly priced higher set, cashing out with a minor loss, back when I bought them, the price i paid seemed nearly bulletproof.
The point being is that the justification for paying the sky high prices is now gone, given that the market is no longer a "sure" thing. There are significant cracks in the wall that are forming, with a potential dam about to break.
While the golden oldies (Taj, 10179, GC, etc.) will always hold significant value due to the rarity and the fact some collectors just have to have the original, nothing moving forward will ever remotely produce returns like previous and based on buy in will likely not be worth the time to deal with in regards to storage and shipping and listing. It could be conceivably possible to lose money... something previously unheard of in Lego investing unless you just went off the rails with RRP Chima.