And why do you assume that any neurons have been damaged? It seems to me that the brain is highly capable of adaptation as is evident by it's function of learning new things at rapid rates during childhood. Epigenetic responses from a very chaotic situation that arises quickly from drug use, like the mass release of neurotransmitters, a situation that someone's brain would never encounter otherwise, seems more plausible to me.
But I do agree with you on the Dopamine aspect to the HPPD question. I have a rather unfortunate opiate habbit and it seems that the opiate effect on the brain releases large amounts of dopamine and this counteracts my dissociation and visuals by quite a bit.