What's the point of ANY luxury good? What can a Patek Philippe do that a $25 Casio cannot? They both tell time. A Honda Civic you bought used for $8,000 will get you to the grocery store just as well as an AMG S65 will.
The comment of "is it just another way for people to try and let everyone know their class" comes off as envy, sorry. Secondarily, I can guarantee you that the 99% of the folks who even know what a Sebenza (or a Strider, or any custom made folder) is...are on this forum right now. The chances of you ever whipping out a Sebenza to cut a thread with it only to hear indrawn breath and "!!! A SEBENZA!!! WOW!" from coworkers or strangers in a public place are slim to none. And yet, people buy them anyway? Why do you think that is? One might posit the theory that, just like every other luxury good out there, people are willing to pay a premium for a high quality luxury item. And I would also guess that most members on this board who bought a Sebenza surely didn't buy them to try to impress others.
So, to answer your question, the point that a $500 knife is worth it is when someone has $500, and they want a Sebenza or other high priced luxury item. Pretty simple.