There is definitely something very appealing about distinguishing the finer details of various aesthetic pleasures, whether food, art, or drugs. If I liked alcohol more, I would surely be a wine snob (instead, I'm a tea snob).
However, I agree with Xorkoth that there are nonetheless very real and important distinctions between all the various molecular permutations. If Shulgin's whole repertoire suddenly disappeared, leaving behind only the old guard of LSD, mushrooms, et al., I could live with it, but I'd be really, really sad, because my favorite drugs by far are all Shulgin creations.
I think the existing research on serotonin provides some really fascinating clues into possible ways to generalize its function (and therefore the action of drugs that target 5-HT receptors). I was just recently skimming through some of the research cited by the Wikipedia article on serotonin.
This study basically shows that, in nematodes, 5-HT causes behaviors associated with food abundance (increased feeding and fat metabolism). It got me thinking: does the growing mental health crisis seen in affluent countries like America result from a disparity between our instincts, which evolved to work in the context of relative scarcity, and our rather sudden (in the context of evolutionary history) wealth?
You could certainly argue that obesity is caused by a misperception of food availability, on some basic biological level at least. Serotonin is critical in modulating appetite, which is why obesity was treated with fenfluramine before we discovered the cardiac side effects. Do mental illnesses like anxiety and depression also result from something that could be described as a false perception of scarcity? Depression is associated with persistent negative self-beliefs. Perhaps the therapeutic value of serotonergic drugs for these mental illnesses would actually be not entirely dissimilar from the therapeutic value of anorexic drugs like fenfluramine, in that they correct a basic misperception of resource availability: in the case of anorexics, the resource in question is calories; in the case of antidepressants, the resource might be something more abstract like creativity or social status.