I recently drove from Annan to Amersham, (and obviously back again a couple of days later), and I found the bucket seats in my BE reasonably comfortable. My back didn't ache any more or less than in any previous car I've owned.
Having said that, I don't think I would pay extra to have the bucket seats instead of the standard ones. At the time of looking, a local SEAT dealer had a Black Edition at a reasonably good price.