Raul

I don't think you own a gun that is 200 years old, has gone through either lots of use through hand me down or has been negelcted and survived a nuclear war.

IMO gun/armor repair makes perfect sense. as others have said, one would replace certain peices for other, more efficient ones and during combat, especially with melle opponents, weapons get damaged. EX, fighting a super mutant and he runs up to you and swings at you with a lead pipe or such, and ends up damaging the parts on your gun, like bending the barrel or busting the stock. So in guns, switching objects like barrels, stocks, handles ,and such, would be feasible, in EW it'd be like replacing wiring and the arrays that are used to fire them, and similar for armors.I'd also like to see it expanded on, like having certain items to be in your inventory like whet stones for bladed weapons, screwdrivers for the nuts and bolts on guns and certain armors, even a small blowtorch to weld on scrap metals to blunt weapons; to effectively put it back together if broken, or make more durable or damaging if in a workable condition, this could work for armors too though. In certain cases it would be possible to maintain/repair without these things but the repairs would be less effective. Also id like to see a system of defending yourself by using the weapon to block melle blows. A case where it could be used would be like when fighting driver nephi and when he swings at you, you could bring your rifle up stop it, lowering damage taken, but increasing weapon degradation.
...... Another idea, finding individual weapon magazines, like when finding a weapon you would clearly only have one mag for it, so reloading it should take longer, unless you find more or already have found extras before finding the gun. in some cases, youd find a weapon without a mag, or find individual mags for a weapon you dont have yet. not a problem for revolvers and most shotguns or older bolt-actions, but important for automatics,

Repairing is very logical. I know that in real life I can fix my broken baseball bats by disassembling another baseball bat.

But, this is the post-apocalyptic future, gun parts would have degraded and rusted, meaning that most likely, your gun would malfunction (i.e. low weapon status) or break. Take for instance the barrel of a rifle. In a non nuked away world, you could buy a perfectly manufactured one, no cracks, fluctuations and the likes. In Fallout, your using guns that have been around for two hundred years, and who knows how many times pieces like the mag-well has been replaced, or if the barrel is rifled how well that rifling has held up, it may have become a piece of crap, causing bullets to jam and the likes.

Edit: Here's how I see the Gun Runner's weapons in game: The slow degrading status of the gun isn't the weapon getting damaged, it's the gun's cleanliness, and by this I mean how dirty the barrel has become. This is when something like a maintenance kit would make sense, but they wouldn't replace Repair Kits. In game, maintenance kits would be abundant or a static item in your inventory that could be used like, 3 times a day, and would be used to repair any gun that hasn't been "broken" beyond use. If a gun/armor finally broke, that's when you'd use another one of it's kind, or a Repair Kit.