I think a maxed sized map is a good idea. It would be an escape from the less than medium maps that are currently in MW3. Large maps from MW2 like Overgrown, Fuel and Derail made sniping fun. I find the sniper class in MW3 to be basically useless since one has to be on one end of the map to be able to properly snipe at someone. Those with military training and those who have actually served in the military would be hard pressed not to agree that Quick-scoping is not sniping and is purely for entertainment purposes and showing off. While I do agree that proper Quick-scoping is a skill, those with modded controllers and marked screens have more of an advantage than those who rely solely on regular controllers.
Getting back on your idea of the terrain regarding bushes, a river, native bridges and sniper towers I think those would be great. Ghillie suits would be in style again! However, I find the idea of two bases facing each other and both equiped with gun towers to be unrealistic.
Logically, a foreign military force building a base near an existing one would be easily detected since a lot of consruction would be necessary. For a native force not to detect such an intrusion would certainly mean that they were meant to be conquered, because of failure to supervise one's own territory.
Perhaps just one base on one side but have 3 crashed Ospreys scattered all around with their gun turrets facing the base. That way it looks like it was an assault gone wrong and Bravo Team has been sent to correct it.
All in all I like the idea of having a max virtual surface area. I'm sure that will affect respawing, since spawn trapping someone will not be an issue anymore because they can respawn in a safer area and rush back to the firefight and not have to worry about a cheap victory due to a bad respawn.