Darren, you've struck a very sensible point within your message: how much the type of sales changes the behaviour of the potential buyer.
Though I am no psychologist or anything near, and I have bidded for very few items, I do believe that the BIN type of transaction has the potential buyer mull over the item a lot more. You assess the item better, because you know the final price and can coolly evaluate it against the very value you grant in comparison. So typically you are inclined to want to spend less, generally speaking.
On the other hand, when you're caught in a frenzy of a tight and hot auction with 'standard rules' the actual possibility of overreacting to a previous move by a contender is something that can cause the price to jump considerably and unexpectedly.
I have only once bought a watch with the BIN policy and it felt altogether different.

So I fully agree that a 500USD-plus may indeed be something one should take off considering a BIN purchase.

As for the main question, I am no Monaco expert nor (please don't stone me!) Monaco fan, but checking out Heuers I have seen myself very nice Monacos staying unsold for a long time for their high prices (> 7500 USD). Weak dollar doesn't help of course, as dealers keep on pushing up prices to make up for that...

Cheers.

Fabrizio