I disagree with Joe about the Sebbie versus the 710. The difference is definitly there, but it is in the form of fit and finish, not performance.
The Sebbie isn't more than twice as good as the 710. You pay a lot more to get a little more, as said above. But IMO, it is clearly a better knife. The performance of the two may be very similar, but the Sebenza has fit and finish of a custom level, while the 710 has the same fit and finish as my $30 CRKT. People say that this Benchmade has great fit and finish, or that that Kershaw is flawless. But in reality, they aren't seeing the little details that more expensive knives get right.
To my eye, the fit and finish of every brand-name production folder up until the level of William Henry or Chris Reeve is about the same. Benchmade, Spyderco, Kershaw, Buck, CRKT etc... yes, some are better than others, but they are generally the same. They all have minor cosmetic flaws and occasional lemons that must be returned. These brands do not make perfect knives. They are not in that business, and if they were, they would cost a lot more.
With small companies like Chris Reeve and William Henry, you have to pay a bit more. Benchmade is a big company that mass produces knives and has very little human eyes and hands involved in the process. Chris Reeve is a small company that doesn't do as much volume, and also spends man-hours hand stroping their knives to a perfect polished edge with no grind lines.
Is it worth it? I think both types of knife are worth it.
I don't really care if the fit and finish of a knife is perfect. I love my AFCK, Manix, SERE 2000 etc... they are great bargains. But they aren't perfect. I also love my Sebenza. I paid more for it, and it doesn't perform better than the Manix and SERE, but I cannot find a single flaw on it. I spend a lot more time marvelling over the Sebenza than I do my Manix or Skirmish. But they all work about as well. If you pick up a SERE or 710 and think it is perfect, then you do not need a Sebenza. But I see all of the little flaws in common production knives like the 710 (and they all have these flaws- the QC and tolerances are not tight enough to get a knife perfect unless it is a fluke), so I need a Sebenza to get a different kind of knife fix.
At the same time, there are more expensive knives that do not nail the fit and finish. I think Strider would be in this group. They have fans for different reasons, but are obviously worth the price to many people (I am going to get an SMF soon, so I will have to see what I think once I get it).
A Corvette Z06 (Manix) will perform just as well as, in fact, probably better than a Ferrari F430 (Sebenza) around a race track (piece of cardboard), but the Ferrari costs a lot more. Is it 2-3 times better of a car? Not based on performance. But the Ferrari, simply because it is less common and produced by a small, renowned company, has a certain aura about it. The Ferrari is more special. Ferrari is a smaller company that does less volume. Their parts are (usually) made special from each car and not grabbed from a parts bin to save money.
I respect the Corvette Z06 as it kills exotic sportscars and supercars costing much more in straight line, cornering, and braking performance. The Corvette is a smart buy. But a Ferrari is what I lust after. It is the passionate buy. Is that worth the extra money? If I had it and could afford it, yes. But the Corvettes of the world are worth it, too.
Because of diminishing returns, the difference between a 50 and 100 dollar knife is easy to see (the more expensive knife will likely have better blade steel and handle materials), but the difference between a 100 and 200 dollar knife will not be. The difference between a 100 and 200 dollar knife will be more in the details, and just the "specialness" of the knife and company. A Lone Wolf or Emerson may not be any better than a Spyderco or Benchmade (even in the details), but the have more of a mystique because they are smaller companies. I think that is worth something. When you go up to a Chris Reeve, you get the mystique and real improments in fit and finish (details).
Everyone has their own line of price/performance that they will not cross. How much are you willing to pay for extremely small improvements, or no real improvements at all other than a more respected name? For me, Chris Reeve and many un-fancy custom makers (such as Hinderer, Obernauf, Martin) represent my line. I will not have 2 grand for an art knife with damascus and ivory blessed by Mother Mary herself. But I will pay 500 bucks for a *user* handmade custom because it gives me a feeling that a 710 cannot.