Hmm. Contrary to your thoughts, I must be the biggest 'pure' collector around then as I have never sold a single,bar, round, or coin, EVER, and a phone is a fabulous way to kill time while placing auction bids.
I agree with some of the items on your list. The question is, what is here to stay and what is eventually going to go the way of Beanie Babies? Slabbed numismatic coins will always be in demand, including errors, Morgans, die varieties and other things that some of us may not be interested in but will always occupy a niche. Modern NCLT and bullion items, however, I would place in the Beanie Baby category, along with “first strikes” and other gimmicks.
Just occurred to me, another thing I think as underhyped, even though they're technically not coins, would be "Hard Times" tokens. There's a lot of interesting varieties, and they're surprisingly cheap even in higher grades.
Hard to predict but my hunch is that the people who paid outrageous amounts for toned and lowball coins are going to be disappointed in the long term. The bogus "get rich quick" stuff ("error" coins mostly) only seems to be getting worse but the suckers and scammers can play in their own pond.
Yeah, the only "money" I have earned in the hobby, (in quotes since I never sell), is from PM stuff like buying silver at $4 and gold at $500 and simply age. Most stuff you bought in the 1980s or 90s is worth more today. Beside that, the only reliable way of "making money", (again theoretical since I do not sell), I found was buying into hoards and holding. A recent example is the athenian tetradrachms that hit the market the last 5 years. I bought many around $400-500 that used to be $1500. Well today they are back to $1000 at least as the huge hoard is finally dissipating. Other than that, coins, especially for collectors, should not be viewed as a money making scheme. My mindset is that I buy coins I love and the price I paid is made up for in my enjoyment. I basically "use up" the value in my pleasure. If my heirs sell for some money then good for them, but I spent what I spent solely for my personal enjoyment. I feel most collectors should have this mindset and only spend "hobby money" on coins, NEVER "investment money". The buy/sell spread is way too huge for that to be a profitable mindset.