I just came back after playing around with ambient lighting on my '14 535i, it actually can get really bright even in the lower door bins.
Ambient Lighting is dependent on two things
1. Primarily on the instrument lighting knob setting
2. Secondarily on the setting in the iDrive -> Lighting Menu
The illumination is calculated by adding settings for both i.e. 2+2 = 4, so if you really want the ambient lighting to be visible you have to crank up both!
In my experience, even if you set Ambient Light intensity in iDrive to Max, it still won't be visible until you crank up instrument lighting (the knob near headlight switch) to more than 75%. Btw, the same applies to iDrive screen's brightness, however, it is dependent on Instrument Lighting knob + "Control Display" brightness setting in iDrive.
What I did was set Ambient light to full in iDrive then adjusted the lighting knob so that ambient light was at my desired illumination - think it's at 80-85% mark. After that I went into iDrive menu and adjusted (lowered in my case) idrive screen's brightness so that it's somewhat dimly lit as I don't like too bright iDrive at night.
One observation I made was that although Classic light is more BMW like, Modern (white) actually lights up the lower bins even better at lower brightness setting.