I like history. When a gun was converted to, and presumably used as, percussion that is part of its history. In my dreadful youth I reconverted a North pistol to flint. Yeah, my workmanship was OK but in the process I discarded that drum, with the metric threads which North used.
If one collects Kentuckies one has little choice, as the larger number of flint rifles have been reconverted. I personally do not like modern castings stuck on my rifle but it does not stop me from buying it, if I can.
I have a fine carved & engraved (attributed) John Haga, done by replacing the original lock with an unused flintlock, like those Dixie had barrels of in thee 1960's. Try not to think of it. Then two flints one of which I believe original (rifle #3, pp83-84 Dillin) the other either original or an excellent reconversion. I don't intend to run any cameras down the bore to check.
I own two flint rifles converted to percussion and not in my lifetime will anyone mess with their locks.
Oh, and my Bodenheimer (attributed) is an early percussion rifle made using a converted flint lock. Waste not, want . . .
Well, that's sporting rifles. Whether or not you like reconversions, that's mostly what you are stuck with these days. Its one reason I like flints converted to percussion, there is an excellent chance that they are for real.
To me, a military rifle or musket is a different matter. They are not works of art, they are 3D history. For myself, reconverting one to flint does not simply lower the value, it absolutely destroys it. I would not own a reconverted musket any longer than it took to sell at a give-away price.
I like hen's approach, I just doubt that it would be done here in the USA