What are the merits of owning a dozen $500 guns (or a half-dozen $1,000 guns) versus one $6,000 one?
I can answer that one. Well, I can give you a generic answer, and then my reasoning, anyway.
1: More varied experiences. Owning 1 gun vs 12 means the owner only gets the one experience. If it's a rifle, no handgun experience. Flint, no percussion, ML no centerfire, etc. The experience of (the act of) shooting that one gun doesn't really change that much.
2: Many don't really have $6k all at once to drop on luxury items. Those dozen guns may have been bought 1-2 per year over 6 years time. It's a big difference. Plus if something happens to a $500 gun, it's less costly to replace or just to deal with being out that money.
So for me personally, I like to be a blend of the 2? I've seen peoples collections, just racks and racks of stuff in a room they had built to act as a safe. Or even slightly more modest collections in 1-3 large safes. I'm not that guy. I don't want to have them just to have them. I'd rather have a small collection that I can enjoy seeing, handling, and shooting; without having to relearn the Dewey Decimal System just to find the dang things and remember what I have.
Having said that, my finances are limited. A $6,000 gun is generally outside my reach, and that's if I could even justify it to myself. I mean, if I really truly wanted it, I might be able to sell every gun I own that's in shootable condition and afford it. Maybe, if I put work into private sales and got better than gun store offerings. But outside of that I think I'd be short over $1k. (though if you add up the price I paid I get a bit over. Yay me). So for me, I'd rather slow build, and have a little variety.
In another post you talked about wanting to honor what the gun was built for, and that's to be shot, hunted with, etc. I agree with that statement in general, but I might argue specifics.
Take a nice flintlock rifle. You start with a plain maple stock, quality barrel, plain blue/black steel parts, no carving, no engraving. It's a rifle, and it was made to shoot. It might be attractive, but it's clear that it was made to shoot and no special considerations were made for appearance (well, lets say the stock is shaped in some particular style, but there's no adornment. Just not a slab.)
Now you can make choices beyond that: higher grade wood/polishing work, deep blue finish/case hardening, polished brass parts, metal inlays, pewter nose caps, stock engraving, metal engraving, etc. All of those add cost, but they're all simply aesthetic. They exist to be seen, they don't really aid the shooting, and likely aren't even noticed during that act.
The more of those choices that are made, the less it becomes something built for shooting, and the more it becomes a visual art piece. It still can be shot, but the ratio of shooter/art piece leans heavily towards the art end. Potentially so much so that anything beyond putting it out for display might actually be taking away from it's main purpose.
I'd still shoot it though. Boom, baby, boom.