It depends on the activity. I've seen every high end build add spy towers but never troop towers because eventually you are protected by dtw. For spies once you're emptied out you are a wide open target for steals. That's why people put towers up to create a threshold to protect against a large number of spy actions from smaller spy builds as well as keeping high end spies from unloading all of their spies at 0 risk.
Why am I able to buy a $25,000,000,000 clan with 100 points but when I go to the oracle I would only get around $1,000,000 for the same amount of points?
Oracle has to resell those nobs to pay the bills, albeit a steep loss but there you go. Kidding aside it's because before clans used to be really cheap so when the the higher tiers came out everyone and their mother owned a clan. When they raised the price of clans it started to stabilize a bit, but it's still too cheap in my opinion. Also the cost for how much gold you get from nobs scales from your build and lands that you own, there is a thread by wulf that breaks it down. Maybe it's just land I can't remember as I've been off for a long time.
Relics are dropped 100% from the summoner and smoke signals ebs at the moment. These are equipment pieces that require you to repeat these ebs for scrolls to enchant them.