AoM is, if anything, TOO defensive already. The death star of starting towers means you really can't rush with most civs. No real rushes mean that what you're left with is generally raiding strategies, based on the units that are least vulnerable to the towers - RC and hippikons. Sure, crenellations help out making those towers kill the cav easier - the problem is that that's a static expenditure - you just spent 300 resources which doesn't basically harm your enemy at all, unless he lets it do harm. In the meantime, the resources you spent on crenellations (and possibly the tower upgrade) your opponent will spend on getting economic upgrades, or just aging.
If anything, ES should be looking into options for making maps with no starting towers. That'd be a more fun, dynamic game. The problem is really that AoM has been designed as a defensive game, with the starting towers and the powerful vills. A true rush simply won't work - in order to attack, you must first mass up units, usually at home, then go "raid" - which gets quite boring.
Removing the starting towers from all the maps is a pipe dream, of course - ES won't do that, which is sort of a shame. The game'd be a lot more fun if people would have to actually think to play defensive, rather than getting it handed out for free. Starting towers tend to even out skill levels too - the difference in skill becomes less noticeable because the worse player can simply rely on the free shooting buildings for defense anyway.
Now, ES designed the game this way - with rooks who like to play sim city in mind, and to give them "a chance to last longer against better players, because being blown out isn't fun." I believe an ES guy (Mike Kidd?) once stated something along those lines. Not 100%, but I think something like that was offered as a reason for the starting towers early in AoM. It's the company line. Of course, it seems to ignore, sort of, the fact that the rook won't have a chance anyway - he'll get beat, it'll only take a little longer. I suppose what really matters is the feeling of not being killed off like a bug. Anyway, since ES designed the game this way, they can read posts like this, and say "ah, there are people complaining both that AoM is too defensive and others complaining it isn't defensive enough - I guess our middle way is the right one" - that may be the case, but I'm still far from convinced their analysis is all that good. People tend to play people at their own level, thus the main effect of the starting towers is to extend games between people of similar skill levels, or to make true rushes impossible, which really just makes for raiding, raiding, and more raiding, while trying to out-econ your opponent. Then again, it can also be argued that the starting towers enable fun strategies like going fast heroic, which really wouldn't be possible without them - which is also sort of true.
I simply think there should be standard maps that don't have the starting towers. Lowering tower cost is a really dumb idea, though. Towers are already dirt cheap when you look at unit stats and tower stats, and the fact that towers let you "break the pop limit." Sure, two towers cost the same amount of resources as one migdol - sans the favor. They also have about twice the firepower of one migdol or therabouts, and they can cover a wider area. You can also make 30 towers as opposed to a maximum of 12 migdols, or fortresses, or forts.
I really hope ES does NOT listen any more to the people that already caused AoM to be as highly defensive as it is, however.