I agree, scavenging should be more useful. I once made a suggestion about scavenging in urban areas ->
http://fodev.net/forum/index.php?topic=9317.0What if ammo was scarce, uncraftable, and obtainable only from NPCs like quartermasters from a faction, or the chemist in Adytum, or something similar, and with a cooldown (just like when you buy holodisks from the Followers)? just imagine factions doing TC with, say, Small Guns and Melee builds. They would shoot and switch to knives, spears, whatever, when they run out of ammo. And only one or two drug based powerbuilds.
However, I don't think the idea of crafting is bad, especially basic crafting. I think it is fallouty if you scavenge certain kinds of items and then create something out of it: ropes, radios, spears... but we would need to make basic crafting more useful for our suvival, even at higher levels and for bigger factions, somehow.
And about this:
Farming and buying weapons is very fallouty
I think it would be cool if NPC run shops never sold high tier items, and if we needed to obtain them from NPC factions. And I disagree with you about farming, because I can't imagine a postnuclear wasteland overcrowded with caravans, wandering scouts, etc. Farming should be limited, maybe with longer cooldowns (I understand there is a cooldown for each kind of encounter, or something like that), and/or more severe consequenses to certain levels of reputation.
EDIT: oh and forgot about this
Instead of using repair to fix a weapon using air, why not cannibalize a gun of the same type to fix the gun 20%?
Yeah it would be interesting.
I think this kind of modifications would have a positive effect as you won't be able to just flash an Avenger and rape a lvl 1 bluesuit with it. Because the weapon would be hard to get, its detererioration would be something to worry about at least a bit more, and the ammo it needs should be saved to be used against a more dangerouns enemy. That would be Fallout, in my humble opinion.