I have used some LEDs, but I have not converted a whole game to them
I am usually wanting to change the color scheme on the game, ie Green lights in the Goblin area on Spiderman
I have also used LEDs under colored inserts on the Sterns, Blue LEDs really make the blue insets pop out at you
The problem with using them on Spiderman is that some of the insert lamps are supposed to glow with different intencities, the more times you defete the bad guys the brighter the lamp glows
To dim lights a pinball machine is actually turning the lamp on and off quickly, the quicker the switching the brighter it glows
This is fine with bulbs, as the nature of bulbs (warming up, cooling down) means you do not notice the switching
With LEDs they tend to strobe, (because a LED is either ON or OFF) which can be annoying
