I think it's just important to, with each idea, ask yourself if YOU would continue to find it enjoyable. I have to admit that when I read your details, it sounds promising and diverse, but again, when I actually picture myself playing it, I think it could still potentially get old simply because the player would see a pattern to it, even if the pattern is as simple as no storyline.
The most fun I ever had with Skyrim's radiant quests? Enchanting. Enchanting gave the radiant quests purpose, because since I needed a certain enchanted item before I could experiment with the enchant myself, it actually DID give meaning to dungeon-diving and opening that end-dungeon chest. Every time, my otherwise dull and drab radiant quest concluded with the potential of my character becoming stronger, and that's what kept it fresh. Obviously this eventually died out when I learned all the enchants, but STILL it provided several hours of meaning, and I think that's acceptable.
I think if you were to do this, you would need some sort of factor to keep things fresh; we need motivation, because a LOT of people can't roleplay just for roleplaying's sake. The player needs to stand to gain or see something unique by doing them. This could be literally anything, from a random chance that the enemies wield fairly nice unique weaponry, to doing ~10 of them giving you a "bonus reward" in the form of a unique item, or perhaps a choice of reward that ranges from things players typically get use out of but have no way to obtain (a couple doses of Turbo, weapon repair kits, ~200 rounds of a certain type of ammo, a random weapon mod, etc etc).
A couple suggestions I can think of off the top of my head:
1) Make the reward something other than caps. The players don't need more caps, and the player would much rather loot guns from Legion hit squads and sell those rather than doing repetitive radiant quest. If however the radiant quests offer Turbo doses, weapon repair kits, auto-inject stimpacks, or something else that isn't exactly easy to farm, then yes, the player would prefer the radiant quests to, for example, running around hunting down turpentine, cazadors and broc flowers (turbo). A minor EXP bonus could also be nice, though tbh I think the base game offers plenty of EXP, so don't go overboard with the amount received. Keep in mind though that this would liken the radiant quests to, say...farming organic items to give to the seed processor in the sink or killing NCR troopers for their dog tags to give to the Legion in exchange for supplies. It's not actually boring if you've ever tried it, cause it's a rewarding way to give meaning to some of the more random ingredients like those pumpkin seeds (grab them, turn them to salient green, turn that into broc flowers for Turbo or pinyon nuts for wasteland salad), but I'm just trying to give you an idea of what kind of fun factor this would have.
2) Sit down and think up a couple of unique weapons and armor types that would give the player incentive to do the quests. Make them appear randomly; not sure-fire on every quest, but with minor odds of being in the hands of the target. That way, if the weapons or armor are well-balanced and interesting (and balance can be anything from a Hunting Shotgun with more damage per pellet to a unique Plasma Caster that has more than 80 [censored] item HP that actually deals 5 less damage than the constantly-breaking vanilla versions), then even if it takes a player ~8-10 radiant quests to actually find one, one is enough to give them motivation to keep doing more.
3) Perhaps combine points one and two with weapon mods. Make it so that alongside potentially finding weapons on enemies, the weapons themselves have mods that again, can randomly be found on targets. Perhaps make them more frequent than the weapons themselves simply because finding a mod shows the player that the weapon counterpart exists, then gets the player curious and entices them to keep going. Tying into my above example, if you made a unique plasma caster that had the main attraction of not [censored] breaking every five seconds, mods as simple as reducing it's weight, reducing it's spread or increasing it's DPS would STILL provide purpose to the radiant quests. The mods could either be rewards from the NCR itself or randomly found
4) Alternatively, scrap the idea entirely and go for a more random encounter approach. Random encounters indeed help the game feel more alive, even if they're very simple. For example, I really liked the courier that brings a message to you a couple days after you complete NVB II. Random Encounters don't need to be nearly as fantastic because they feed of off basic player curiousity and a desire to feel immersed. Having a random hit squad employed by one of your former (or current) targets come after you does both, because the player thinks "who the hell are these guys!?" and then feels completely immersed when the game acknowledges through the random encounter that the player did indeed kill a certain target in the past or the like. (perhaps the leader of the Shadow company, for example?)
But yeah, I think suggestions 2-4 are more a question of time more than anything. Kinda hard to gauge how many unique weapons one person can think up, how many can be implemented or the like. The overall point though remains: Skyrim's radiant quests svcked because they lacked purpose. They completely lacked storylines, and the coin rewards were just rubbing salt in the wound, cause wtf coin grew on trees in Skyrim. No one will do the radiant quests if they only offer coin while offering significantly less story than the other targets. Radiant quests need purpose to work.
Another thing I'd mention is you probably want to somehow make it clear to the player which quests ARE radiant and which ones are not. No matter how nice you can manage to make the system, some people simply will not like it at all, and I'm sure those people would appreciate some sort of signifier that tells them which quests are NOT unique. The computer terminal that lists the bounty names off sorta does this, but perhaps if there were another way? Hell, perhaps stick another NCR Ranger in the office building who "handles the smaller bounties" so that the player has a different NPC entirely that they need to go see for the radiant ones. The different names on the posters ("Speak to Captain Larry Skull" OR "Speak to Ranger Dingledong" on the poster for the radiant ones) or simply picking up the quest itself from a seperate NPC would get the point across.