Buying cheap, low-value coins in the hope that they will go up in price, under the impression that, logically, they ought to go up in price eventually, is "speculation". Which is a fancy way of saying "gambling". The lack of certainty results in the human part of the equation: people and indeed entire countries do not always respond logically to their situation.
As with any gambling event, if you spread your bets far enough, you should hit a winner or two.
Let's look at some historic scenarios. Back when the Soviet Union collapsed, people said "Now there will be a new wealthy middle class of Russians who will be keen on buying up Russian coins. So Russian coins ought to go up in value.". And they did, though perhaps somewhat slower than originally speculated. And I don't think anyone really expected nostalgia for the "good old days of the USSR" to rise so quickly.
As Middle Eastern oil boomed, people said "All these wealthy Arabs are going to be keen on buying up Arabic coins. So Arabic coins ought to go up in value.". But they never have. There simply isn't a "coin collecting culture" that has arisen in the Middle East to soak up the supply.
So let's look at some other markets. China? The new wealth of resurgent China "ought to" drive up the price of Chinese rarities, and it has to some degree, though there are still two things holding it back: the proliferation of fakes discouraging amateurs, and the remaining tendency of the Communist State to see anyone showing interest in pre-Communist China as subversive; it is seen as "un-patriotic" to collect coins of anywhere but the PRC.
Africa? It was long presumed that interest in African coinages would increase once post-colonial Africa stabilized and the people became wealthy enough. This, too, hasn't happened yet, and in my opinion likely won't within a century. Latin America, likewise.
I think your "best bet" is to seek out countries where there is a historic baseline of coin collecting, but which for whatever reason, that baseline is being suppressed by current circumstances. China is the most obvious example here: a country with a strong tradition of coin collecting that's even older than it is in the West (the earliest known coin catalogues are from China, written 1500 years ago), but where the current government's policies actively discourage it. Should the government radically change, then we would see a clear resurgence in native Chinese collecting, which would in turn see massive price increases for the classic rarities.
The other thing to remember is this: many of the low mintage "modern rarities" in world coins are not truly part of the history and culture of the country named on the coin. Large minting corporations (Franklin Mint, Pobjoy, etc) and quasi-privatized government mints (RCM, Perth, etc) use these countries as "flags of convenience" whenever they can't find local government support to legalize whatever their marketing departments might dream up. Future coin collectors in Uganda, for example, are unlikely to be interested in collecting the "Ugandan coins" made by the Perth M
int some years ago, that feature
designs that are entirely Australian rather than Ugandan in nature. Australians don't and probably won't really want them either, because they're not "real Australian coins" and therefore aren't mentioned in Australian coin catalogues. So I would predict that such coins would usually fall between the cracks and remain unwanted by everybody.
Of course, people aren't logical, as I mentioned earlier. Logically, the Perth M
int Redback Spider coins "from" Tuvalu should likewise have remained in the doldrums and not soared to $2000 apiece. But they did.
That's gambling for you.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis