I think the small tolerances are a small part of a larger picture. Alone, they are not very important. I agree that lesser tolerances do fine in general.
One of the largest--if not the foremost--benefits to any CRK knife, Sebenza included, is that you know if anything happens to it, CRK is there to fix it. When you break your 10 year old Spyderco, Benchmade, etc., at best you'll get a different model or store credit. Moreover, there have been threads where people said they had trouble getting replacement parts for foreign-made, current-production Spyderco models. None of that is a concern with a Sebenza. The service and the associated peace of mind that goes along with the knife makes it worth the price. I wish I could buy everything I use as often as my knife with such service to back it up.
Back to the tolerances, they go to show the knife is extremely well made, meaning it won't be bad engineering or manufacturing that causes the knife to stop working. Service to fix any problems that might come up *can* be great, but it wouldn't be worth it if it kept breaking so as to need to be sent in. It's the service and the precise manufacturing together that make each of them meaningful.
Furthermore, given that a Sebenza is meant to last decades instead of months or years, the tolerances are more important than for a knife that will be a shorter period, since better tolerances reduce wear and tear with normal use. Do they need to be as good as they are? No, probably not. But, if I'm buying something to last my lifetime, I'd rather have it made as good as possible.
Since everyone loves car to knife metaphors: I would gladly pay much more than what my vehicle cost me if it meant the tolerances of a CRK and the service to back it up. Really, what price would you put on a car with everything made with the engineering and manufacturing that goes into a CRK knife, and with the lifetime service? A car that will run for my lifetime? Sign me up! That goes for anything I use often, actually, not just a car; I'd gladly pay much more than I do now for the "CRK treatment" to come with them.
I'll end with something I glossed over so far. Not everyone is looking for a knife that will work as good as they got it on the day they die. For people who will be using a different knife in a month or a year than they are now, a Sebenza is definitely not worth the money because they aren't going to take advantage of what it offers for the additional cost. I suspect this is where a lot of the strife surrounding it comes from; to the question, "Is the Sebenza worth its price?" the answer is not "yes" nor "no" for everyone.