If we look at the "package" of the HE6se, it includes the HE-adapter box worth $99 and the cable is $250 more (if the spare parts in the HiFiMan shop are the same as the original parts). In other words, apart from the updated design including headband and connectors, the HE6se has added value of $349. In that context $500 extra isn't that bad.
Another angle people don't consider is that part of the purchase price is paying to provide support and maintenance, in this case of older technology that might be even more expensive to support compared to newer ones.
In many cases like this, bringing back "older" technology and re-selling it is actually more expensive for the manufacturer because of these support obligations.
I did end up purchasing the HE6SE and it is currently en route to me. It has been stuck in Canadian customs for over a week now, unfortunately. I will provide impressions as soon as I get them. Like others have said, I suspect it will be enough to just look at this thread to see if these headphones are right for you. The big wild card are the headband and the comfort - which Hifiman proved they could potentially botch with the HE 560.
I will update the thread as soon as I have them.