I find towers usefull in late games, where all resources have been sucked up, and all you have left is the stone. This is even better if you have an enemy island with all the stone on it as well, as you can get BT, and advance.
One stone miner can get you all the stone by mid iron, so its not a waste once you can afford it, just one guy can mine all the stone and youll have stone late in the game for towers if need be.
Also, towers are very annoying, you have to get cats to take em out, and even then if your not carefull, you can lose a couple of cats. Most people rush with archers, soon after bronz, so towers help lots then, but dont rely on them, have an army ready yourself.
I once had a great 2v2 game, I was phoenican, friend egypt, against a summie and minoa on medit. my friend droped at about 45, and we were actually kinda losing, just managed to kick the guy off my island, but he had a great defense guarding the pass, cats and HA and Gtowers, so it was hard for me to get through, so I built like 30 armoured eles and ele archers for backup, and disembarked in the middle of the guys island, I took him all by surpise, and won the island with my initial forces. All the resources on every island was out, nothing left but some fish in the middle of the ocean, but what helped me win most, was my Balista Towers that I built to hold back my enemies ally from coming to his aid.