Excellent post. I have been buying Lego for several years. I don't sell at the moment, my view was always 'one day I'll resell if I find myself out of work', yet up to now am still in work, so the Lego accumulates in the loft, but I can see that more people have got in to this, and all of the above points are well made.
I think it's nowhere near as easy as 'read a few forum threads, buy licensed sets, sit back and wait', which largely probably worked a few years back, but is more likely to burn people now.
Key is to find a strategy that works for you. I have changed dramatically what is heading up the stepladders in to the loft these days. I have a different strategy that I am confident in, but it's still a guesstimate on my part, but one based on 15 years experience of Lego, so you need to have faith in yourself.
I will say that I do think more than ever it does pay to have diversified investments which for me absolutely can include some physical product or investment. Fiat money, currency or whatever term you want to use is under genuine pressure. Lots and lots of countries have debt to GDP at very high levels, even above 100% in some cases, very difficult to repay back. Default isn't exactly an option due to the impact this would have on confidence across the world, so sooner or later we'll probably get some genuine inflation to inflate some of the debt away, that's my working hypothesis! Of course again I could be wrong, but I feel currency as an investment is rather vulnerable and volatile, and will remain so for some time, so I don't mind having money tied up in physical product like Lego, even if physicality also has its own different risks. It's the old adage, do your own research, balance your risks etc, etc.