Towers aren't worth cost wise unless you are using them to fire into your opponets base resource location or are almost at pop, because towers can add damage while not taking any population space.
You need one always within range of another usually, and even then, I've seen skilled players take them down very easily with a mix of units and few viligers.
Try instead to balance your economy to stay very aggresive with food units and get heroic. My last few games my eco looks something like 17 food, 6 wood, 8 gold so I can get both alot of rc and a few valks with a 9 to 11 minute advance, in which building hillforts is much more cost effective then afterwards.
The only exeption would be if you get locked in a classical fight with a hip building greek or later in heroic dealing with camels/elephants or prodromos and research crennelations. That can pwn them, especially with safeguard researched, as I think two towers covering each other with cren up and safeguard can do some pretty fine damage to them while they try to take them down. It becomes less effective it seems the more pierce armor ups they get, although it should be noted that prodromos die very severly to tower fire(as they suffer from both low pierce armor, hitpoints, and the 2x bonus of cren), when it hits them.
Nick: Eten.
Gods: All of them!
Vanilla.