I've seen quite a few collections sold over the last 12 years, including some major collections of the more obscure Freeman and Gouby varieties and it does feel to me that there aren't that many (if any) new variety collectors with money to spend.
My theory in general is that we Baby Boomers are the last generation with disposable income together with the nostalgia for the pre-decimal age, in coins, music, stamps, cars etc etc.
When we all pass away I wonder whether the next generation will be interested in the things that we hold precious - all collections may slowly fade away to nothing in value. It's interesting to watch the various antiquey programs and see how items come in and out of fashion, e.g. brown furniture (which I still adore). I'm not sure if they actually ever come back.
As for pennies, it does seem that the proof coins more than hold their value. The 1839 proof penny is not all that rare but continues to rise in prices realised at auction. I suspect that obscure varieties may not be a great investment prospect.
Maybe varieties of mobile phones are the next collectable ?