Lemme throw in my $.02...

First off, using Jefferson to defend the current interpretation of what is referred to as the 'separation of church and state' is a mistake. The "Wall of seperation" letter was written to calm the fears of one group, an intimate conversation, if you will, and not neccessarily intended for longevity.

What many people don't know is Jefferson was fundamentally against the bill of rights. Yep, The fellow who is seen as the archetect of the separation of church and state would have rather it not be part of the constitution at all. That's certainly not to say he didn't agree with many of the ideals, just that they need not be part of our constitution.

Another interesting thing is Jefferson while saying there would be a wall of separtation between church and state, meaning in the particular document that the federal government would not interfere in matters of religion; did not believe that that also applied to the individual states. Congress did not include the states, and at that time we still had a tenth ammendment. So certainly, Alabama would have the right to display a religious monument, despite the first ammendment, which explicitly applies to congress.

What has changed in constitutional law between then and now is the current interpretation of the commerce clause. Which fundamentally voids the tenth ammendment (which gives the states all rights and privlidges not explicitly granted the the federal goverment), by stating the federal goverment has juristiction in any matter that can effect trade between states (read as: absolutely everything)

To wrap this up... invoking Jefferson seems to be a flawwed arguement for either side, as not only was it a peice of legislation he disapproved of, but the Danbury letter is also rather ambiguous in it's nature. The determination of whether it was a ploy to garner support or an outright declaration rests solely in your opinion of the matter.