I can only assume that the always on headlights have massively contributed to the degredation as the other two halogen projector headlamp cars I've owned (a 1998 Ford Cougar with 150,000 miles on, back in 2013) had way better headlamp output than ANY of the significantly newer S40's I've owned.

I also had a 2003 Toyota Avensis with halogen projector headlights that again with 165,000 miles on (in 2017) were way better than any of the S40's I've owned.

I almost feel that Volvo should offer some kind of discounted replacement for the headlights on these cars.

Guys from US were planning a mass recall petition/lawsuit when it all started, but dont think it ever happened. I suppose it fell under goodwill of manufacturer as technically lights are provided and technically are road legal (as approved before car is made road-legal in any country) so its clearly Volvo dropped the ball like "yea, we dont care" and then 3years later redesigned headlamps for FL model (wit still pretty cr*p output).
ah well... every manufacturer I gues has their highs and lows...

Halogen filament bulbs within a projector lens are always bad but even the Volvo's with factory HID's aren't the best by all accounts.

The standard set ups were always aimed too low right from the factory, lifting the beam angle to just within the MOT tester's equipment helps a bit but overall they're just rubbish and lots of people have been forced to modify the units themselves which is pretty poor if you think about it from a safety point of view.

hid bulbs with 55w ballast
 

so I read a lot of issues with these headlights
I work through the night and all my driving is in the dark
replacing to hid couldnt be easier I certainly don't get flashed by other drivers
they are as bright as new cars too
if your worried about the dreaded mot then change them back but your find the beam pattern is ok
this really is a no brainer
kits available from £15 online
would recommend a 5000k bulb
hope this helps
my headlights are great now with a super white colour