People alter their appearance because they feel it makes them more attractive according to their perception of the modern standards of desirability. In past generations women strove to stay out of the sun to preserve a more pale appearance that was considered more desirable.
People would tan because they believe it makes them look healthier, more active and fit, and more like the popular images of models in the media. Some perceive more pale to be more sickly, kept indoors, or whatnot. I am not saying either is right or wrong, but that is the general fashion idea nowadays (at least in the US--in other countries where people are more multi-toned they often seek to be as light as possible).
Fake blonde hair is often a result of trying to recapture what your hair used to look like when you were young. For most people who have blonde hair as children their hair changes to a more mousy, dishwater, or gray blonde as they become adults. They want to recapture the more platinum or golden tones. For those who didn't have blonde hair to begin with they are just following fashion trends or trying new things.
The fake boobs and plastic surgery are again an attempt to mimic the current social ideal. People often feel more self-confident if they think they are more physically attractive so they modify their appearance to match what they think is most attractive if they can. In general people want to desirable and admired and many think improving their physical appearance is the best way to achieve that.
If it primarily brought negative results instead of positive results people probably wouldn't do these things, but as long as it works, or they think it works, people will continue to do it.