Considering what a depreciation hit the R129 has taken, I wouldn't worry much about its resale value.
A forum member here (MBenz, who doesn't frequent this site much these days) did the upgrade to his 300SL to the 97 look, including rims. He posted pics of the reconstruction process and the efforts turned out great!
I'm not much of a purist, as my ML is body-colored, which was not standard in 99, and I will put the Euro lights on my W124. I plan to body color the lower cladding on my wife's SL eventually, and possibly a rim upgrade.