It has just been suggested to me by a fellow guild mate that the benefit of getting the watchfire towers', if you only get a few (less than 10 for example), applies mostly in a situation where you belong to the latest age, so that considering that you have the chance to defend your city with same age or higher age troops as your potential attackers, that defense boost really can make a difference, specially along GB that also give that boost.
(I'm sorry if I didn't explain myself too clearly, English is not my first language and sometimes it's hard to build phrases and transmit their meanings well).
I suppose this is not very wrong, but keeping in mind I'm mostly a farmer and when it comes to GB I'll probably skip those related to war, do you think spending the eggs in 5 towers would be a waste? I think so, but I'm afraid I'm missing something out.