Are Eternal Darkness and Super Mario Sunshine really worth over $70 each?
For now, yes. Both games seem to have shot up in price in the last couple months. They used to be around $40-$50. Perhaps they'll fall back down. Perhaps they'll stay insanely expensive.
On each game's page, on pricecharting.com, there's a chart that goes over the historical prices of the game. CIB = Complete In Box. So just click on that at the top of the price chart.