Like lots of other people said, I use Warden and High Tower quite often, usually on the same outpost.
I never looked at stables but I imagine I'll start using them on unit hubs now.
Caltroops seem silly since enemies can just counter the outposts.
The offensive and defense upgrades seem OP and slightly cheesy to be honest because I believe they provide an even higher boost then being stationed in a city would?
Never really looked into the extra growth option, will definitely be using it now.