My concern is that by fixing the camera it will actually depreciate. I am used to dealing with collectible firearms where any modification from the original condition will actually detract from the value even if it's in operable
camera collectors are concerned with condition and whether it works.
If it's condition is already rough, and it can be made usable without altering its appearance or original equipment (except the shutter material if that is what it needs) and you have a repairperson you trust, and you want to use it, I'd say go ahead.
Your repair costs will add to the value of the camera, since any camera that does not work has servicing cost deducted from its value by any buyer. In addition, you will get to use a vintage camera, and cameras are tools that like to be used.
The only exception to this rule is cameras that are really, really, honestly, no kidding now, don't pull my leg on this one, mint, and I mean M*I*N*T.
Those, after sitting around for 40 years, probably don't work anyway, and aren't meant to. They are safe deposit box fodder, jewelry for billionaires.
Replacing the shutter materials does not detract from the value of the camera because shutter curtains are replacement items, meant to be swapped out of they break or wear out. It's not the same as "fixing" a vintage rifle by replacing the barrel.
I have a 1931 Leica I (C) that had a rotten shutter curtain when I bought it for $200 30 years ago, and needed a new one. I had a new shutter curtain installed, now I have a working Leica I (C) that just had another overhaul (every 30 years need it or not) and is probably worth a pretty penny. Not that I care, I take pictures with it.
If it's ever sold the buyer won't care how new the curtain is, only that it works.