While an interesting idea, tying tangible rewards/buffs is probably a bad idea, especially in the form that you're proposing with tents and campsites remaining in-world for extended amounts of time. As for RP purposes why not ask for a stationary campfire minion in the same vein as the wind-up sun/moon or cushion minions?
Many of the buffs you proposed already exist as FC buffs which anyone can join one if they choose, so if anything I'd agree with making a temporary sanctuary zone centered around the campfire for party members as it'd be an overall more balanced reward but one that makes the existing towns still relevant since you can log off in them and still get the bonus while campfires wouldn't. Others you suggested upset grind balance or would in fact become necessary and not a spontaneous sort of activity.
Overall not a terrible idea but needs more thought to balance.
