Has the woofers faded due to sunlight ? It's very common to see lighter and darker areas on the cone - it has been like that since new.
Those original SEAS (in some Beovox S60 VIFA) woofers are practically impossible to match with modern day drivers. Original drivers are generally sought after and no doubt the best for the speakers. Remember they were not off-the-shelf ones but actually designed to B&O's specs and if any changes would have made the woofers a better fit for the speakers, it would have been done already. Yes, you can buy woofers that are more up-to-date but on which specs will they be better ?
Anyway, if you replace the woofers with a different type, you have to change the crossovers and possibly other drivers to match the change.
If you decide to sell them I'm sure there will be many takers. They don't make them like this anymore.
Martin