Bitcoin is the first-mover with the big network effect. Litecoin (at least currently) offers no meaningful technical advantages, but it has 4x the supply. Thus, the upper-bound, even if litecoin succeeds in being "silver to bitcoin's gold" is that it'll be worth 0.25BTC. But that's if they both achieve the same popularity/market-cap. I think you have to drop litecoin's upper bound by *at least* an order of magnitude to account for the fact that bitcoin's network effect is overwhelming when talking about a contender that offers no real technical advantages.
So that takes us to 0.025BTC per LTC as a reasonable upper bound.
And as untested as bitcoin is, both technically and economically, litecoin is even more so, so throw that additional risk into the mix too...
The thing about LTC is that it's spurring a new generation of GPU miners that are buying and hoarding it, much the same as with BTC two years ago. LTC supply halving is also happening in less than two years. These two things alone will be likely be enough to ensure the longevity of LTC.
I think we will see prices well into the double digit USD in the next 2-3 years, with volatility similar to bitcoin for 2011-2012.
The way to get rich in crypto is to just buy one that is heavily adopted (BTC/LTC), stick your coins in a cold wallet, and come back in a few years during which you completely ignore the market.