Sweet lens! I love mine!
I'm actually of the opposite opinion regarding UV filters. B+W filters are very very nice to be sure, but they're actually only slightly cheaper than most front elements. It cost $150 to replace the front element on a 28-300L, which is actually a more expensive lens. Now, I don't actually know what it costs to replace the front element on an 85L so I could be off-base. The other things to consider about filters is that they're pretty tough to get off lenses in some cases of damage (I know this from experience!). Also, scratches and dings to the front element rarely affect image quality. As for resale value, just go ahead and send it to Canon for element replacement if you want a better sale.
Just my opinion, though!