With much high fashion clothing, you get what you pay for. That is, you know your clothes are going to be well made with quality materials, and in some cases, by hand.
With the Lacoste shirts, in this case, you're also paying for that alligator logo, you're paying for the Lacoste brand. People pay extra for brands that are going to be recognized. In my mind, I also feel that people are paying for, i don't know how to explain, the feeling you get when you know people are saying "Ooh, he's wearing Lacoste..." It makes you feel special, makes you feel like a big deal that you're wearing high fashion.
Personally, I don't own any Lacoste shirts. I think it would be nice to have one, as a special splurge for a special occasion, but I don't feel like a loser since I don't have any. I don't think it's worth it to have a closet full of Lacoste. Besides, if I did, people might take me for a rich snob.... ;)