This is some good investigation--thanks for getting to the bottom of it! Nice to know that KL isn't off-limits.
Sorry in advance for this equally long post. I will say that there are some drawbacks to intentionally clearing one's shields in KL. In addition to the lost reward, you won't get to see who has been raiding you so you can at least return the favor.
The bigger downside to this approach, however, rises from the question of whether it actually helps your neighbors to raid you at all. In creating events and FP this year, EA has really made an effort to diminish the need for and offset the advantage of keeping a list of many good neighbors, instead seeking to make the few-neighbors or single-player approach more viable. In crafting the rules for this event, they've been even more transparent about it: defeating an invader gives you 5 times the reward of defeating your sparring partner, so stop sparring already, collect your FP/donuts, and go defeat some invaders. (and this is a topic for another thread, but I bet the random button will be back in the future. Not only does it make single player more viable, but it accomplishes a major objective of their neighbor system--to hock premium items).
Because I understand that, on my end, the nerds are ultimately going to waste, when I raid neighbors, I do it either to help their scores or to send some sort of a gesture (thanks for being awesome). Thus, I preferentially try to save more nerds for neighbors who appear to want to be attacked (lower score, houses not undefended), and I absolutely never raid Other Springfield or my feeder towns because I perceive it as a total waste of nerds that helps no one and yields significantly less than random attacks. If a neighbor were to go to KL to clear/surrender his shields from my attack, not only would he never get to see my gesture, but he'd effectively turn down the gift--however meager--and the nerds would go to waste.
I realize this is all a circle of neighborliness and goodwill, and I'm not sure the best approach to being neighborly. An alternate solution would be: help your neighbors by visiting for FP, but don't clear your houses at all--this way they'll know you don't need the gold, and they can instead attack randoms. Of course if everybody did this, we'd have no randoms to attack. :?
