Exactly! So it begs the question...is a knife a trinket or a tool?
Yes, a knife is a trinket or a tool--that's the Chinese way to answer that question, isn't it? Not focus on the "or", but answer in the affirmative if one of the conditions is met.
For me, a traditional knife is both a trinket and a tool. It is a trinket in that I always prefer a nicer example of a pattern--something with bone or stag or nicely-grained wood, and something that's designed well and put together well. But it's also a tool that I use several times daily. So for me a knife has the utility of a tool, but it's also something more, something that is aesthetically pleasing to me that I can appreciate using.
In a way, the question you ask makes me think of Rorschach Tests. In the same way that the ink blots are what we make of them, traditional knives are also what we want them to be. For some, they are utilitarian tools and nothing else. They might get used to cut, but also scrape, pry and screwdrive. They might get (what I would consider) horribly abused and mangled or broken, but that is why the owner values them--to do what needs doing, and do it with one pocket tool. They also might get taken care of really well and only used to cut, but the owner sees them as tools and nothing more. Others might value knives as art, or as investments, or as statements of success or anticipated success, as commodity fetishes, as extensions of self, and so forth. These are all other extremes of the utilitarian's answer that a knife is only a tool. I think our various answers reflect how we perceive ourselves, and maybe what we are trying to convince ourselves and others that we really are.
I like traditional knives because they use a minimum of steel to get a job done. There is no excess, wasted steel; even when the edge dulls say, cutting cardboard, they still work really well because the blade stock itself is still so thin. By contrast, most modern knives have thicker steel and will not cut in this way as well, especially when the edge dulls (please note that this is my own preference and a common task for me, others use knives for very different purposes). This is the utilitarian side of me.
I also like traditional knives because there is an abundance of natural materials in the handles, and the handles look well integrated into the overall knife--not like they are screwed on as an afterthought. Traditional knives are designed really well. The shape of the handle and the integration of the natural materials into the overall knife just seem right. to me This is the "trinket" side of me.
I have about 20 slipjoint knives. Some I keep for sentimental reasons, some I keep because I frequently use them, and some I bought to try out, but have since found out they aren't for me and I'll eventually sell these or pass them along. 20 knives is too many for me and I will winnow that down a bit now that I know my own preferences. My folding knives range from Case-Bose and Dozier on the high end, to Case, Queen, Canal Street & GEC on the low end. For me, these are at affordable price-points that will not scare me from actually using the knives, but not so low that I feel I'm scrimping on quality construction and lessening my own enjoyment of using the knives. This paragraph says a lot about how I see myself and the tools that I use. I suspect that when we get to the core of collecting or using knives, we see quite a bit of our personalities and values reflected.
So, is a knife a trinket or tool or both? You get to determine what a knife means to you and what parts of you get reflected in that decision. It sounds like you're going about it in a really thoughtful way. Good luck and let us know what your answers are.