I don't know exactly the math behind the item degration mechanic, but I had to restart my first 0.1.7.0 game due to not being able to afford to repair the starting gun.
I used both the starting gun and crossbow to kill the rats, and went back to buy lockpicks, haxxor and ammo for the second half of the power station quest.
When I got back to the monsters I noticed every shot was lowering my aim, all the way down to 20%, which makes it harder and harder (more bullets and faster degration).
After figuring out it was the low durability, I went back to buy a repair kit only to find it cost 950 (have mercantile) which I couldn't afford. Since both my gun and crossbow was in bad shape they were worth a lot less. So I couldn't even sell one of them to make a repair.
I did "forgot" I could use PSI, so I restarted instead.
On the second playthrough, I used my bare hands to finish of the rats whenever I could, to save bullets/repair cost. Getting back health was free...
Anyway I find the basic repairkit to be too expensive, a smaller and cheaper repairkit (about half effect and cost) would be better.
Putting a repair/maintainance (the gun) quest following up the shooting range quest would make players mindful of a repair mechanic ingame.
After my first 0.1.7.0 completion I find the item value/durability be off.
Many ranged weapons was worth far more after repairation, so I "had" to do repairs before selling which was a bit tideous and silly.
Armor durability is far stronger than weapon durability (guns atleast) . I have only done one armor repair during the whole game, because it was looted with low durability.
For the ranged weapon loot, I rather find slightly higher durability on them and less ammo, that way I can atleast try it out or use it for a bit on the field before returning.
I could as well put my thoughts on the grenades here.
I don't like how they work now. Usually when I need to use a grenade it will be tossed at the beginning of a battle. If it misses I just reload...
I rather they hit the area targeted like before, but it's effect depends on your throwingskill vs enemy dodge/evade and range from the center. (I can't remember an enemy evaded a grenade before). Of course you can still reload until every enemy is hit... but I find it less likely if the damage scales in a appropiate way.
The ones near the center of the explosion having harder to evade, and the damage could range from full, partial to none.
If your throwing is better than enemy evade/dodge, there is a good chance to hit the ones at the edge with full damage also. If you are are bad, then even those at the center only take partial damage.