Hi Lim,
I've got a friend who drives a 300sel, w126. A friend of his did a simple mod to his instrument cluster, simply by shorting the potentiometer. In other words, the dimmer doesn't work anymre and it's on at one position. If you don't turn the dimmer a lot, which I guess most people don't, you could try it! By the way, the brightness increases by about 20-30% more.
Alternatively, you could change the cluster housing, which might costs you more!
Just my opinions!