What is the purpose of any kind of upgrade........

All good questions...

One answer is that very few components that are designed are considered 'perfect' by their manufacturers. Certain parts could have been made better in the initial design; however, it would have pushed the price of the product up too high. Thus, a manufacturer offers an upgrade for the product a year later instead of making a whole new upgraded product (or line of products).

Also, some components are modular and are designed for upgrdeability. In many ways for the consumer that pays nearly full retail it is advantageous for them to buy upgrades to a product as opposed to buying a whole new unit.

I hope this begins to answer your questions.

KF

In addition, technology is always improving. Look at the chip sets in DACs. They have been improved and changed over the last ten years. Look at Steve McCormack and the older DNA amps. He states that the design was the best he could do at that price point and nopw better parts are available to him to upgrade his designs that were not availabe several years ago.

Well yes and no...often an upgrade or "signature" model is designed around one of the manufacturers best selling items...and the upgrade is often "trickled" down from a higher model...such as the Vandersteen 2ce signature which features a tweeter from model 3...among other things...but to answer your excellent question...is the additional cost worth it yet? I have mixed views...I will use Vandersteen as an example...you could also use Meadowlark Hotrod...or a number of products...for these...the upgrade models cost roughly 4-500$ more(APPROXIMATLEY 1/3 OF THE ORIGINAL PRICE)...and since they are applied already to a speaker in production...the additional cost for the manufacturer is not that much greater...the kicker: are u really making a significant gain in performance to justify the extra...in absolute terms...the gain is marginal...we are afterall talking about VERY GOOD SPEAKERS to begin with...however...if u see yourself owning these speakers for a considerable amount of time...and want the most current design...then the upgrade is worth investigating...although you will be severly testing the law of diminishing returns

Mamba, I've upgraded my turntable through the years as the improvements bacame available. I'm glad I did. I've owned the piece for almost 20 years and it performs equally with what is available new today. Upgradeability is a strong reason to buy an item in my book.
Patrick

Why should I buy such a product anyway and pay again for something that was already paid?

Don't think that you are paying twice. The point is to spread the component out to more price points, knowing that audiophiles tend to upgrade. I think it is easier than going through the buy-sell-buy hassle, if you happen to really like the component. The manufacturer benefits from keeping an intro buyer buying from them.