Fear not, the quests expire after a while and the annoying icon disappears. Just as frustrating though, I've a quest that requires land units to complete in my manticore nuke city but for some reason I cant use the manticore for the quest.
Its obvious whoever came up with this does not play the game with any seriousness, I'm not screwing with my city setup's and wasting farm space for this.
No, some guests are actually quite nice. Of course, it all depends on with whom you hang around with. It also depends on why you want to invite them. For a birthday party, invite anyone you want, providing they give you gifts. For a bow and tie party, invite only those who you think will behave like human beings and not crazed orangutans. Be sure to to provide plenty of food and drinks for your guests, maybe some activities, and you'll find that your guests might turn out to be nice!
The quests are really very helpful! I do agree that I dont want to mess up a city setup, but there is always a way around that! choose the other choice! the rewards gained from quests help out quite a bit if you plan properly.