If litecoin would get the same adoption as Bitcoin, it should be priced 1/4 of the BTC value
True, but the adoption level at this moment is completely different.
There is not many things / services you can buy with LTC, except for gambling.
For the general public, they may have heard of bitcoin from news.
They may find it interesting, or laugh at it. But, at least, they are aware of such thing.
On the contrary, they may have never heard of litecoin, or they may just consider it as "ahh, another bitcoin-like stuff".