This is a timely topic for me and fun to follow. (And for the record, brunette for me!)
Different folks arrive at their love of this stuff along different paths. I completely understand someone interested in living history, recreating, reenacting or representing a specific era to want their rifle to look age-appropriate for the time and place they are portraying. However, someone whose primary interest is the visual impact of the object or that "something" that is sought by collectors of art or antiques may have a different perspective. As may the hunter or competitive shooter to whom only the function and performance of a longrifle matter and to whom any aging is equivalent to intentionally damaging a fine tool. I see all these points and there is merit to all of them.
Personally, I like the look of a bit of well done aging on some pieces that could equally stand on their own merits of design and function if finished "as new". But then, my primary interests in these old longrifles at this point in my life are not reenacting or historical trekking - I just enjoy studying, making, carrying, shooting pieces that I like.
I agree that aging can be, and is often, carried too far - it should never be carried to the point of damaging the functionality, lifespan or safety of the item. And I have seen many examples where it was. And many examples that just look deliberately beat up, without capturing the warmth and feel of an antique. You can spot a piece that has been boiled too aggressively in Clorox from across the room, and many such finishes really don't resemble any kind of age or wear you see on antiques - even "relics." There are many people who attempt aged finishes on guns, bags and horns these days but there are a few who are much more adept at it than others. I find that those who do good restoration work on original items and are skilled and knowledgeable with regard to matching old finishes and materials tend to obtain the most plausible looking aged-contemporary work as well.
Trying to get back to the original question, as to "why" some folks like aging, it is hard to put into words. Last week I got to examine what was in my opinion the finest aged contemporary hunting pouch set I have ever personally handled, done back almost 30 years ago by one of the first and best contemporary artists to do ever this sort of thing. And it just exuded something I find very appealing - the same vibe as some well worn antiques. I don't know if I can explain why. It just looked right, not contrived or overdone, in spite of it having many simulated repairs and wear built into it.
We tend to think in terms of "wear and patina = age in years". And that is why some find carrying an aged or worn looking contemporary piece implausible. But following the "use" line of thinking, I will throw this out there. If I my objective was to accurately portray a longhunter in Kentucky in 1770 carrying a late 1760s style rifle would I find it unlikely to have what looks like 50 or 75 years of age and grunge and use on it already - absolutely. On the other hand, would I find it plausibile for a well worn 1770-made piece to be used daily and passed down in a family to pick up 10, 25, 50, or 100 years of wear within the period of it's working life - 1790, 1820, 1850 etc.)- also absolutely yes. There are so many examples of guns, bags and horns that were carried and used to an extent we cannot comprehend today. Multiple generations carrying them every day. Used, cherished, broken, repaired, broken again then restocked or cannibalized into another piece that was used until it too literally was worn down to almost nothing. And still treasured enough that some family member thought to finally put it up and keep it for future generations. Although I am sure there are some of you who have, I will conjecture there are very few of us who have ever worn out the straps on a pouch - much less carried a horn enough to cause visible wear on the inboard side - or a curly maple stocked longrifle long and far enough to literally wear down the wood on a forearm and cause a polished "rippling" effect to appear, or wear through to the ramrod hole. But how many, many originals you see with this sort of wear. Rough scraped home-made horns with the inboard side polished flat and slick as glass from wear - worn through in many instances - wear carrying through the wooden plug; a groove on the neck from strap wear, two or three types of strap attachment devices replaced over the years on the plug, etc. Wear on a rifle from being carried countless miles on horseback. This sort of wear occurred during the working life of the object, not the last 100 years it spent sitting on a shelf or in an attic after being put up for the last time. And I think this type of feel is what the best of the "aging" techniques strive to, and can, convey on a contemporary item and is what is appealing to those of us who like that sort of thing.
Guy