Flying across the atlantic if I was offered an upgrade for $250-300 I would seriously consider taking it. If I was offered the same amount to take a downgrade I would seriously consider refusing it. For > $500 I wouldn't buy/refuse it in a heartbeat.

Of course airlines don't sell business class TATL seats for < $500 -- except if you're buying them with points. And they certainly don't sell first class tickets to Asia for $700 which is about what the difference in points is worth. So if I'm ever going to fly first class for a big vacation trip that'll be how.