I don't believe there is niche for a successful mom-and-pop cryptocurrency. We don't know how many successful cryptocurrencies there will be (including zero) but it will be closer to the number of very large businesses than mom-and-pops. That could still be hundreds or even thousands (or a much smaller number of course), but one way or another they will be very large or will fail.
I think there will certainly be niches. Collectible card games, multiplayer games in general, music-centric coins, cause coins (like Gridcoin but for many of them for different purposes) etc....
I even think there are successful niche coins that exist today with low market cap but with solid development, solid marketing, and/or solid innovation.. such as Qoura, Crypti, Siacoin, Bitcrystals (although its overvalued atm), GetGems, etc...
It is much easier I think to have small (but still substantial enough) adoption and be somewhat successful than to knock it out of the park. You are claiming that every cryptocurrency should try to knock it out of the park, or end up completely worthless and there is no middle ground. I don't like setting money on fire though, and that is what everyone is doing if they follow this logic. Only a handful of coins will win, and if yours doesn't then it's dead- game over. I don't see the appeal in that unless you're simply pumping and dumping, and I'm definitely not betting much on the fact any alternative cryptocurrency is going to knock it out of the park (even Litecoin.)