It is an interesting idea indeed, but I think using Occam's razor rule in explaining the phenomena leads to conclusion (and there are two scientific opinions I obtained that are backing this position: one of biochemist, another - pharmacognosist) that it is either lymphatic, endocrine or pheromonal response of serotonergic depots within the synaptic agitation range by psylocybin, causing these systems to over-activate. Being a true hematofilic parasites, mosquitoes' ability to detect any deviations in a normal biological profile of the host is the questions of life or death. If the insect misinterprets this "signature" due to changes caused by the tryptamine, it might consider such masking a sign that food is not fresh or edible anymore, given we can take as a working assumption that blood-sucking insects posses yet undiscovered ability to sense such metabolic processes via some unique sense or other means, therefore treating inebriated person or animal as potentially "hazardous" target who is in the process of detoxifying from perhaps a harmful substance and therefore is not worth risk of eating. This could be a simple evolutionary defense mechanism that spares both parties from unnecessary poisoning.

HBWR left a friend and I to realize and say to each other simultaneously, "They're landing, but they're not biting!" -- we were talking about mosquitos of course.

Pure anecdose.

If you want to use occam's razor here, it looks like you should be slashing your decently complex answer