This is a great post.
I come at it from a slightly different perspective, thinking more about the collected object and less about the collector, although they are related obviously.
My experience with collecting is more formed from my interested in vintage bicycles, so some of my language will be transported from that domain. I'll try my best to translated into knife-knut as I go as well as to cycle round (ahem) to David's question about why this is more true about Buck than other brands.
In terms of knives (and bikes and probably with cars), I think there are 4 basic groups:
1) ORIGINAL - In knives, this is often NIB with papers. There are cycling equivalents, to be sure. I'm sitting on a 1982 Fuji America in 99.9% original condition. It's really flawless and was an amazing find. Sort of like finding an old Mustang on blocks with the stickers still in the wheel wells.
2) RESTORED/PERIOD CORRECT - Some parts of a bike are wear items and it's expected they'll be replaced at some point. The question then becomes, replaced with what? In bikes, we talk about "period correct" restorations, which allows for parts from the era of original manufacture of the frame. Repainting the frame is the next question. Original and hammered is one thing. Restored with non-factory paint and better protected is another.
3) DAILY USER - Some old bikes still get used on a regular basis. Parts could be from any era. Is this collecting? It is of a sort. It's the kind of "collector" who believes the bike was meant to be ridden and the knife meant to be used.
4) MODIFIED/HOT RODS - Some non-period restorations go well beyond just making them capable and modernized. They become highly modified hot rods. Here is a link to a picture of a c1980 British Mercian frame with high end c2005 components. The frame had to be "stretched out" to accept the new drive train.
http://home.comcast.net/~pinnah/dirtbag-bikes/hot-rod.jpg
This is somewhat equivalent to the Buck modifiers like Yellowhorse and many others.
Now to cycle around to David's original question... I think some brands (intentionally or unintentionally) drift towards one kind of collected object or another. If you were a collector of vintage Raleigh bikes or Rene Herse bikes, it would be correct to collect original or period correct restorations. The old Raleighs were made as complete bikes and it's sensible to think of them in this way. Same could be said in the car world about, I dunno.. Ferraris. You don't see many modified Ferraris. For that matter, you don't see many Ferraris that have been driven hard or a lot. Garage queens. My sense is that a lot of Case or GEC collectors of this type.
In the bike world, it's silly to talk about an "all original Trek". There's no such thing. Trek got it's start selling bare frames and any competent cyclist was expected to select his or her own parts to build out the bike to suit their tastes. Buck's custom shop is nosing up to this in a much more limited way. Harley's have this in spades. Harley actively encourages and supports an entire cottage industry in customization and modification. A stock Harley is a sad lonely thing owned by somebody too timid to bend it to his or her will. It's like a stock '70s muscle car. What a waste of potential. How sad.
IMO, Buck knives are primarily either daily users or modified/custom. For things/knives of this sort, getting a spa treatment totally makes sense to me.