Engraving is like a tattoo. It is irreversible and the looks depend entirely upon the taste of the owner. Unlike a tattoo, you can sell a gun. The new owner of the engraved pistol will rarely dig the piece because it is not their own design.
If you have a gun engraved, do it because you love the look. If you do it because you think your friends will like it, you are wasting your money. It is one way to make something that was mass produced unique, but beauty is in the eye of the beholder.
I am nearing the status of "tattooed freak". Some of my ink makes people scratch their head and think "***?". I like it, and I get new work done at least once a year. I don't get tattooed to impress others, I do it for myself. The same rings true for guns. If you like it, DO IT.