my 2 cents based on observations of my dads collection and my own.
Temperature in msia is the biggest killer, our so called from room temp is more like 28-29C indoors, pretty bad for wine and for liquor it accelerates the off gas of the volatile components, older liquor kept like 10 years all lose their 'hiongness' when you finally open it.
Then comes evaporation, over time even sealed, the bottle just slowly evaps out and you can see it slowly getting lower. My dad has bottles from the 80s and some of them are like a quarter gone. Some shops i see try to mitigate this by shrink wrapping the bottles.
I try to keep my own bottles at 22-24C to try and mitigate these.
On the topic of Japanese whisky, pretty much my hobby. Managed to stockpile a whole bunch of Yama/Hibi/Haku. The way i look at it, like LVMH, Suntory won't be reducing the msrp prices, so no point looking back at 2015 prices. Right now i've stopped buying at current MSRP as i think the market has stabilized and i dont think Suntory will be raising them anymore. Pretty much all my stuff is bought at MSRP except for the Hibiki 12s and 17s which i bought via auction. Have a full set of the Y18, H18 and Hibi21. Passed on the Y25 and Hibi30, too rich for my wallet.