I'm a firm believer that God made everyone how they are meant to be whether that be hair color, eye color, teeth, skin color, body type... everything. However, we are also supposed to be good stewards of what we are. Yeah, I wear make up, dyed my hair once, I go tanning occasionally, and I work out. Does that make me a shallow monster? I don't think so. I want to do the best with what God has given me. I admit that there's an element of self consciousness that makes me what to look better and dress to impress, but that's not the core by any means.
And, here's something else. Us women are very pressured to look good for the men of this world. We have to have thick eyelashes, plump lips, even skin tone, nice hair, nice teeth, and a certain amount of skin showing to even be noticed, even by the Christian guys. This is wrong, and both sexes are to blame.
As for breast implants alone, I don't think it's wise unless for reconstructive stuff. It's a severe body modification. It welcomes the wrong kind of attention that a Christian woman should not crave, although sometimes it's hard to not crave it. It's a personal choice and personal conviction, but I'd think long and hard about what I was really trying to accomplish if I was ever thinking about doing that. It's for sex appeal, and we are not to cause our brother to stumble. And if I know anything about men, breast implants would cause most men to stumble in most situations.