The only way some other cryptocurrency will overtake bitcoins is if it brought something new, so you would not have to compare it to bitcoins. Why get a copy when you can just use the original?
Why get silver when you can just get gold? Why get a Honda when you can just get a Ford? Why get a double-cheeseburger when you can get just a cheeseburger?
I take it by your generalizations that you either A) don't understand the differences between Bitcoin or Litecoin; or B) you understand them better than I, have come to the conclusion that they don't matter, but refuse to explain why in any sort of detail.
Gold is like 1500 $/ounce, silver is like 30 $/ounce, so if you want to buy in increments of a couple hundred dollars, then silver might be better for you. Until a satoshi is worth a significant amount there will be no need to make a cryptocurrency with a more granular unit than bitcoins.
If I drive a honda and you go out and buy a ford, it does not make the road any less useful to me. But if we each pick different cryptocurrencies, then they are all less useful because less people will accept them.
A double-cheeseburger adds benefits to the cheeseburger (more meat), and so people want it.
To me, the differences between bitcoin and litecoin seem superficial. They have a different number of total coins, but that just affects the exchange rate, you just divide by a different number when converting a price from USD to BTC/LTC. The blocks come faster, but you need to wait for more blocks to get the same confirmational surety, so you end up waiting just as long anyway. The difference in algorithm is no difference to me, since that is all under the hood so to speak, until one or the other is cracked they are the same to a user.