The acrylic tray is very easy to scratch, in my experience. Wet mounting inherently leaves some residue. (If you don't believe me, place a drop on a clean sheet of glass and let it dry for a week. You'll see a spot.) Cleaning off the residue would ultimately lead to scratches on the scanning try. Like Guiherme, I use a DIY glass tray for wet mounting. If you're going to wet-mount everything, then it probably doensn't matter, as the new fluid should dissolve whatever was left from teh last time, and you won't need to clean the tray too often.

I'm really glad that you solved your scsi problem!