A classic question indeed ...

Technically, even a dirty LSD has such a minimal amount of other stuff... i mean, what is active at that dosage...

But there's much we don't know  - as pointed out , specific interactions with the impurities, and also much more subtle things far from the reach of science at the moment

The magic hides in the small cracks of our modelling of reality

What i got from people deeper in the field, what that the precursos used (either natural  from ergot, or a complelty different route) influence the results ; the more synthetic have all the objective effects,  but doesn't have the spark. I tried both kinds (without knowing what is what) and the empirical results fits with that idea - but unfortunatly the dataset is too small... oh noo.... we gonna have to test that again...