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.