That is truly expensive and not something I'd ever contemplate.
Considering the changes, this new model could well be worth the upgrade. Check these out, and ignore those who make outrageous guesses and ill-informed assumptions.
Audio Research Reference 6SE Preamplifier
Audio Research: When SE Is Really Special
Audio Research REF 6 to REF 6SE upgrade.
UPDATE””””””””” I just got off the phone with Audio Research about the REF 6 to 6SE upgrade and I was told that the price of the upgrade went up from last year from $3500 to $5000. I was pretty shocked. Also he said that it will not have to be done by the service dept as they have a guy who strictly does Ref 6 upgrades. as all parts are in stock and it will only take 14 days turn around time.