Add ons or upgrades are never likely to increase it's value. I would only make the changes because you want to, because you'll get more out of the car as a result. There is nothing in wrong in making the car your hobby; all hobbies are sad and expensive.

Beware that many changes can reduce both the saleability and the value of your car. Many buyers seek out originality and are suspicious of changes.

I too really like the 8 hole rims on your car. I think they really suit the R129.

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JJ Rodger
2013 G350 Bluetec
1999 SL 500
1993 E300 diesel T
1990 190