if you somehow manage to destroy that whole set of towers at level 4 and don't then go on to rapidly win the game you're doing something wrong. 

That would be a handy tool for someone to make. A web application (in flash maybe?) that has miniature versions of all the maps as well as tower placement options so that you could quickly generate a map with indicated towers or locations and hotlink it to the forums.

I might just give that a shot.

@OP: Personally, I think that the map control granted by pushing towers is always going to be worth the (what I would imagine to be minimal) xp boon to the enemy.

nah, if you can get those outer towers down you damn do it. its a huge advantage in holding the flag if your tower is still up (giving you a defended retreat point) but your opponent's is down. you can pursue him very far out of the lane, often its enough extra pursuit distance to get the kill. 

and having your creeps march a bit further up is fine as well. you just have to go farm on the new battle line, which is perhaps slightly more dangerous than the original battle line since its further distance to retreat back to safe territory, but hey, you're winning anyway so it shouldn't be a problem. 

There is no reason not to destroy the towers. First of all, unless you are killing creeps yourself, the enemy creeps still meet in the middle. Second of all, there are two towers (and possibly a fortress with trebuchets) in range of the creeps in the center, so the enemy DGs are actually less likely to get to them before they are killed (being near the health crystal aside.) Not only that, but by destroying the early towers you basically have free reign over the lanes, especially if you have a tower rook setting up shop just out of range of the enemy melee towers. It's way better than the enemy theoretically having to walk 4 seconds less to reach your creeps when, and only when, you are actively farming the enemy creeps in that lane.

I think the gold is actually 30, although the experience is pretty good (not enough to make it worth leaving the creep lanes to kill towers, but enough that it is a huge bonus if you are still creeping with AoE skills.)

Huh. I could have sworn I got EXP from towers... oh well, guess I just forgot. I don't kill towers much the way I've been playing lately (Ooze UB. )

It's 300 gold, no exp.

Pretty sure you don't get Forts on Cataract. The only map that I can think of right now that adds forts later in the game is Crucible, but I could be wrong. That's also dependant on the game mode, although I'm not sure in what way (could be good to know). Also I know I saw archer towers pop up in mid game on another map... not sure which though; maybe Leviathan? Anyone have a link to a list that shows how all the maps/modes function in that regard?

Pretty sure you get no xp or gold from tower-killed creeps. Would be interested to see this confirmed, though.

I'm pretty sure you get XP and Gold for every creep killed within your sight range (though I'm pretty sure that is split if there are multiple DGs.)

I remember something about how having minions kill creeps for you while you were not there would get you a gold bonus, but nothing for XP. I can't really remember, but I'm pretty sure if you are nearby, tower killed creeps give you EXP.

It's still useful to kill them, though. Saves your tower a bit of a beating.

the only way the enemies would get to much xp from the towers being destroyed would be if you had bought priests or something, buying them that early is probably not a great idea...

also if you like the enimies towers dont destory them

I do it all the time and have had it done to me. You get xp and gold for all enemy creeps dieing around you, regardless how they die. You get more gold by "tagging" them, doing at least 25% damage.