Benedikt is actually quite vain in regards to his appearance, at least for an undead. He appears about as intact and groomed as is inhumanely possible. In fairness part of it’s due to his use of Light magic which makes him painfully aware of any growing decay. But careful observers will note he seems to act abnormally visicious toward any attacker who deals significant damage to his face. Likewise his civilian wardrobe contains many an immaculate and opulent outfit.
If pressed on either habit he will explain that as someone who frequently represents the Forsaken in dealings with the living these appearances are necessary for his work. This is a half truth at best but he lies as much to himself as he does the questioner.
A lot of this is due to his humble beginnings in Strahnbad. While he was better off than most children- he certainly never starved at least - he was always quietly jealous of the nobility his father served. Undeath can change a lot about a person but some things, like a petty and childish desire for flamboyant finery, die hard.