Firemaiden:
This is a great idea for a thread, and rather than reproducing it here, I'll refer you to my essay on this subject on my website (tarotseeker.com) at
http://tarotseeker.com/Renaissance.html
(There isn't very much to the site yet. It's under construction, but I hope to have it up and running this summer.)
Neoplatonism is a tricky subject, because it wasn't so much a formal school of philosophy as a synthesizing and harmonizing tendency. In that respect, it was kind of like the modern term, "New Age," another attribution that signifies a tendency rather than a specific philosophy that one can pin down.
But there are certain generalizations about Neoplatonism that hold true, and I've attempted to deal with them in my essay. I'm also convinced that Neoplatonism was THE philosophical engine that produced the esoteric content of the early tarot cards. I know some people here think that I believe tarot was originally "just a game," but that's not so. The trumps, at least, have esoteric content in abundance -- in spades, you might say.
I am equally convinced, however, that tarot was never the vehicle for the transmission of a secret doctrine of some sort. Neoplatonism was anything but secret, and the symbols it and the early trumps employed were part of a universal, pan-European vocabulary of images. It was the common currency of these images which, in part, lent the early tarot its spiritual power.
Plato believed that reality is indecipherable to the majority of people who encounter it, but as far as I know he did not believe that the cryptic nature of phenomena could be unlocked by any secret doctrine. Plato simply believed that most observers were unable to penetrate the veil of surface appearances which the Hindus call Maya. Neoplatonism, like many other religio-spiritualist approaches, aims at piercing the veil. But you don't need to know any secret handshake to be able to do that. All that's required is superior insight.
Anyway, why would someone use universally comprehensible symbols to transmit a secret doctrine? The idea is ridiculous. It kind of reminds me of what one comedian once said: "I got home last night, and somebody had stolen my house. I guess I shouldn't have left it out in the open."