Well. I heard back from the senior consultant at the law firm, and mixed news. The lawyers did agree that they could win a cancellation of my contract, which would require that Diamond report to all 3 credit bureaus that the account was closed and marked "paid in full", but they did not think they could win litigation against Diamond for additional funds (I wasn't interested in that, so wasn't too upset at hearing it) AND they will not guarantee that they can get a refund of what I have paid.

All for a flat fee of just $3500. If they could guarantee a refund, I'd go for it, as the refund would be more than the fee, but I don't have the ability to pay that much without getting the refund. The consultant also suggested that I contact the credit card company I used for part of the down payment and contest the charge. He said that most likely, they will suspend the amount for a couple of months as they investigate, but then return that it was a valid charge and reinstate it along with any interest that might have accrued. So, not really seeing a winning solution there.
I emailed the hospitality management contact and informed her that I had received a package that contained a partial copy of my contract. I explained how I knew it was incomplete, and asked that a full copy be delivered to me. I also mentioned that with the growing list of errors and mistakes, that the entire transaction was crossing over into fraudulent business practice territory. Not sure that it will have an effect, but I just couldn't resist. I did manage to tone down the snarkiness of the email quite a bit. *sigh* And it was such good snark too. I saved a draft, just in case I need it for later.
While I was writing the final draft of the email, I did some research looking for the exact correct phrasing I wanted to use, and discovered (or realized?) that the ARDA has a website and a consumer information contact. I am thinking of sending them a comment as well and seeing what happens.
On the forward looking front, Diamond has until 12 April to respond to the BBB complaint. Don't know what good it will do in the long term, but at least it will be out there and public.