Just a final follow up: IT WORKED. Went in to BB weekend before last to do the exchange. Coincidentally, the UN40B6000 along with other 2009 models were being clearanced out that weekend to make way for the 2010 line. I called before we went over because the UN40B6000 had been pulled from the BB Web site. They had exactly one left in stock (!), so I told them to hold it, not mentioning that it was going to be for a warranty swap.
When we got there, we explained the situation at customer service and gave them the confirmation #. We intimated that rather than take the set they might give us, we wanted credit toward a new set, noting that our LNs3251D had been top of the line in its class when we got it and we were looking for something similarly top of the line now. The managers excused themselves to confer for a bit. We wandered around the TV section, noting that the UN40B6000 was now clearance priced at $1,100. They came out and offered us $1,000 in credit toward a new set, which I thought was very generous considering this was for a 4 y.o. 32" 720p set.
But my wife was not satisfied. She proceeded to negotiate with three managers and a sales rep for 20 mins to get them to front the $100 difference and give us the 40" 1080p LED set in an even swap, arguing "it's the principle" and "technically we're entitled to $1,400 because the warranty says 'will refund the full original purchase price'" (not mentioning the fact that it only promises that if they can't replace the set with something commensurate). I just kept my mouth shut, and she finally won out. All we owed was the $200 for a new 4-year warranty (obviously we were going to get this!). Amazing!
So the lesson here is ALWAYS buy the BB warranty!
Ironically, the 40" set proved 1/3" too wide to fit in our cabinet (we knew this going in), prompting a complete rearranging of the room (not to mention the purchase of a new piece of furniture for the A/V equipment, a new media cabinet, and removal of the old hutch we were using to house both). I had briefly entertained the idea of getting the UN46B8500
(LOCAL DIMMING LED!!!), but there was no way to fit a 46" set, even with our new open arrangement (the TV is in a corner now on top of this