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

Honestly, like you 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 more of an, 'I like the content that you post/I share the same interests as you' type thing.

It depends on how you look at it. If you think of becoming someone's fan as "friending" them, then maybe you wouldn't want to remain their fan if they didn't reciprocate. But others (like myself) fan people because they like their contributions or agree with some of the comments they've made, so it doesn't matter if they don't fan me back or even if they're no longer active here.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 you feel strongly about removing someone who didn't fan you back then be my guest. It doesn't matter to me in the long run. So I am in a similar boat 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 or value of adding as a fan here. It's not like friends get extra access to privacy or something. So, I just fan people if I have enough respect for them. And if someone adds me first, I usually add them back as an act of formality or common courtesy. The whole add as a fan thing is nothing but a boost of ego here or sense of security/insecurity. The blocking system is somewhat useless too.