Current btc/ltc value ratio is about 39:1. Gold vs. silver is around 64:1 right now.
Estimates I've seen would be 5x silver extracted from the ground vs. gold. Similar to the 4x in LTC/BTC.

Based on those numbers Litecoin appears fairly valued assuming a similar gold/silver relation.
Silver does appear undervalued currently based on historic ratios (In the ballpark of 40-50:1) assuming a mean reversion occurs.