Quoted from mbaumle:

Playfield planking seems to be sorta common on this game for some reason, look out for that. Also, the clear plastic part of the ramps located *just* behind the light lock standups tends to get beaten up and crack. It's not the biggest of deals though, since you can buy metal protectors to hide the damage.
Checking the ramps and boulders is a biggie. Replacements are costly. Often the "boulder garden" boulders are broken or damaged. Again, replacements are tough to find, and again, costly.
Someone mentioned to me when I was buying mine, to look out for matching standup targets. Since they're the "3D" type, they tend to break, but not often replaced with the proper style.
Look for lost mine kickout damage. Usually, there's playfield burn somewhere around the river class lights where the ball slams into the playfield.
Finally, check the upper playfield where the VUK drops the ball behind the upper right flipper. Cliffy makes a protector for this area, but it's usually beaten to hell and back on a lot of games.

Quoted from mbaumle:

Yep. They're all Diamond plate.

I think the cabinet art was originally silk screened, but I'm not 100% sure though. I couldn't tell you about the blue, but I've noticed that faded White Water cabinets have a slightly yellowed looking bigfoot, where he should be brown.