Well having only been seriously collecting DC for a year or so, I've only had a year of following price trends for the console. That being said, I've noticed the price disparity amongst titles can be a huge gap. For instance a Power Stone 2 or like you mentioned above Cannon Spike can hit the 100+ dollar range at times, yet grabbing a similarly good game like Crazy Taxi or Soul Reaver can be had factory sealed for a fraction of the price.
I will say that I have watched Shenmue rise in the past year I've been following prices. Picked a CIB for 15-20 dollars back six months ago. Its nearing the 30-40 range now depending on where you look. I would probably jump on that one soonish. Another one that has seen a price spike since I've been following is Illbleed. The game's quality is up for debate however it's looking to be one of the more pricey ones these days.