Sol, I have a very high ph. It's a constant problem I have with all of my precision tools. They turn black as a result of my handling them. All of my Starret gages, etc, that are not stainless oxidize at my touch. Even tempered cutting tools I use, such a gravers and chisels, will wind up with a finger print on them from me once the protective film of oil that I must constantly spray them all down with gets removed from use.
-And I have no issues with a worn palm rest like the OP on my two year old 9200.
Aside from being a jeweler and working on carburetors, and I also landscape. Operating a backhoe or a shovel or building a stone wall, it makes no difference - my hands are very rough.
But I wash my hands before I use my computer. And I use my computer about 4-5 hours a day!
So, while I completely agree the ph does vary considerably from one person to the next, I don't believe that it's every caustic or acidic enough to break down the paint used on the palm rest. I maintain that this is the result of grit trapped in the skin of the user... simple dust.
I do believe, however, that Dell did make a big mistake by not clear-coating these parts to offer better protection for the rather soft paint they did use.