My 450sl has bright turn signal indicator so it is possible for this model. I think also that a brighter bulb (if available) can not do any damage to the plastic because they are used only for short periods and they will cool off of a little because they are flashing but that is just my thought.
I once had with a boat that the control lights where also very dim. When I check the problem I found out that the inside of the reflector was dirty. It was a little static and dust was attracted to it.