I put one of the 6 LED high power festoon bulbs (40mm) in my VW and it is very bright, pretty close to the Luxeon output. The 30mm bulb only has 2 LEDs so will probably be proportionally dimmer, probably someplace between a 3W and 10W incandescent bulb (stock is 10W in the dome and 3W in the door).

In my VW, the LED really was an improvement as the stock setup just has the bulb shoved up into a hole in the head liner and there is no reflector at all, so 90% of the light ends up above the headliner. The Toyota dome light has an attempt at a reflector but it is not very good. The Luxeon and high power SBL LEDs have an internal reflector/lens and scatter light out in a 180 degree pattern, so put all the light down and out with none wasted.