At the moment there is no way to greatly improve beauty. I'd like my character to have a perfect beauty score ! ^^
But starting at 40, it's not currently possible, you can do a one-time lab improvement to 60 (iirc) and that's it. Maybe a repeatable way with a high magic cost would be nice for endgame. That way you can choose between improving your slaves or hunt for those perfect beauty "natural" ones.
Lorewise it would be a great amount of magic used to rejuvenate and reshape face and body to improve beauty. Possibly also a way to heal some traits like scarred, crippled and mute.
And/Or, as a more evil option, a sacrifice of a slave (or several) to use the vital essence for the same effect (it would need some balancing so you cannot just recruit plenty of cheap slaves for that).