I love watching academics and conspiracy theorists haggling for their pet theory.
And I had never thought of Bosch as a contemporary of Leonardo da Vinci, so I live and learn.
On this detailed Bosch website by Adam McLean, there is a quick review - overview - of many books on Bosch, and Ms. Dixon's alchemical theory gets dismissed, along with books trying to tie Bosch into esoteric ideas from (say) the Anthroposophy people...
He covers all the 'interpretations' from Jung to astrology and 'secret Cathar' - and dismisses them. He doesn't seem to have written up the 'druggie' one (ergot poisoning, St Anthony's Fire, or deliberate use of hallucinogens like Datura, or Belladonna or whatever).
I think I might invest in his DVD 'course', which apparently has high quality images, and avoids interpretations to concentrate on the painting itself. 120 minutes of video. And his Alchemy Website looks interesting, too. Lots to explore...on rainy days...
*You may also find something useful at this other Bosch resource, although I haven't tested all the links.
Oh, and one obvious parallel that I haven't mentioned. The fact that The Surrealists embraced his work, and Dali (in particular) seems to have employed some of the same kind of techniques and imagery. Here's Anthony Christian on The First Surrealist. He seems sure that Bosch was just having fun at everyone else's expense! But then again, he reckons his psychic friend has chatted to Bosch about it!
And here's Philip Coppens on Bosch
Either way, he is sometimes said to have been the spark that ignited the surrealist movement of the 20th century, which would produce modern greats such as Salvador Dali. Dali knew the works of Bosch (who was furthermore highly popular in Spain) and felt compelled to deny the influence: “I myself am the anti-Hieronymus Bosch.”
And finally, the entry for Bosch from the Hitch-Hiker's Guide to the Galaxy (H2G2):
Think of mixing Fellini with David Lynch, sprinkling in a little James Joyce, and having it all put on canvas by Salvador Dali. Carl Linfert, Hieronymus Bosch, 1989
and the H2G2 link for The Garden of Earthly Delights