look for any wear by the lost mine kickout - there is a decal you can install but I've noticed that the colors in the decal may not match the color of the playfield (due to fading/other).

Upper playfield - look for wear by the upkicker - Cliffy has a good protector for that to prevent further damage.

Planking - yup. I recently picked up a WH2O (second one I've owned) - the second one has some planking. The first one I had did not have planking.

on my playfield, there is a little planking near the entrance for the disaster drop ramp.

If you are referring to the Disaster Drop ramp (on the right side of the two green targets) - I just picked up a repro ramp from Starship Fantasies - nice ramp (riveted and came with the decal).

Here's the ramp. (called Suicide Canyon on Starship's website). It came just like it looks (decal supplied with the ramp, but I had to peal and apply the decal).
http://www.starship-fantasy.com/ramps/W-Suicide-Canyon-Ramp

I recently put the Mantis protectors on my WH2O. I wanted to protect the ramps by the lock targets - I also installed a new disaster drop ramp. No problem installing them.

same here.

Hard to say without pics. I have one that I'm contemplating selling (about $500 above the range you noted) - it has the topper though. Condition is subjective but I'd call mine a players condition machine .

Great game - love all the ramps .