Do 당신 think I should un-fan all those people on this site who never fanned me back?

Honestly, like 당신 said, that's up to you. Personally, I wouldn't but, like, that's because I'm too lazy to do so and don't really see the point. I don't really unfan people unless they persistently bother me.

Frankly I've always seen fanning as less of a friend thing and 더 많이 of an, 'I like the content that 당신 post/I share the same interests as you' type thing.

It depends on how 당신 look at it. If 당신 think of becoming someone's 팬 as "friending" them, then maybe 당신 wouldn't want to remain their 팬 if they didn't reciprocate. But others (like myself) 팬 people because they like their contributions 또는 agree with some of the 코멘트 they've made, so it doesn't matter if they don't 팬 me back 또는 even if they're no longer active here.

I personally wouldn't bother as it would take up time I don't care to use. If 당신 feel strongly about removing someone who didn't 팬 당신 back then be my guest. It doesn't matter to me in the long run. So I am in a similar 보트 as Flicker.

It's up to you. I wouldn't do it as it's a waste of time and energy. I never understood the point 또는 value of adding as a 팬 here. It's not like 프렌즈 get extra access to privacy 또는 something. So, I just 팬 people if I have enough respect for them. And if someone adds me first, I usually add them back as an act of formality 또는 common courtesy. The whole add as a 팬 thing is nothing but a boost of ego here 또는 sense of security/insecurity. The blocking system is somewhat useless too.