yes, designer brands are a want and not a need. yes, there are certain products that seem (or are) outrageously overpriced. but no, many people that pay for designer products are not in fact crazy.
there are, of course, many ways to look at what a decision to buy designer means. but from an economic standpoint, when you boil it down, the consumer basically is a buyer of a buyer.
you, the consumer, pay for a particular taste--that is, the taste of the buyer who determines what constitutes the brand. your clothes/shoes/chosen items are thus selected for you.
accordingly, if you have an appreciation and taste for high quality, authenticity, and style, and money and time are of no consequence, it would likely be to your interest to travel to that particular country/region known for producing the best of that particular item and buy it there from the locals. that way, you are basically seeing the same choices the brand buyer sees while essentially crafting your own personal brand. that, to me, seems like the ultimate luxury.
although--traveling can be expensive, and sorting through all those choices can be time-consuming. not all of us have that luxury of traveling around the world and being our own 'buyers.' that's where designer brands come in. the premium we pay on these products is both the time and money saved and the value we place on the corporate buyer's taste in substitute of our own. the opportunity cost of not being that front-line buyer then becomes largely subjective, as individual preferences determine the cost to be anywhere from minimal to excessive.
value, therefore, is also subjectively recognized when your expectation/willingness to pay exceeds the listed/market price. it then follows that the realization of value occurs when you take advantage of this arbitrage opportunity (i.e. make the purchase).
so whether consciously or not, many consumers of designer brands are actually behaving rationally in terms of their own economic interests. clearly, notwithstanding many other contributing factors, economic sense does not equal fashion sense, and the multi-faceted emotion associated with buying/wearing/using designer can really be a curve ball. but that would be opening a whole other can of worms, wouldn't it?