If I may be allowed to haul in the original model, and how it appeared in '60s broadcast TV, something
very odd was going on behind the nacelle domes. I never even saw the spinny things before cable TV (and its better reception), just an odd, multicolored, raging fire. When you look at photos of the insides of the model's nacelles, that was surely the intent; Christmas tree lights, yes, but endlessly refracted with shards of mirrors.
When I was a wee tot, watching it all in the very first reruns, often in black and white, I always assumed that the nacelle caps were windows onto the matter/antimatter anihilation. I still believe that.
Plus, that's a lot more fun than TNG's gurgling potbelly stove.