Yes it has a significant effect. Because you won't get online automaticaly (in case of missing rescan) to the "Automaticaly used networks" if your connection is down. No active wifi = less battery consumption. But you should not have services in backgrounf that always need the connection (twitter, skype, auto mail sync...).

One week in rare use ist possible for me too.
N9, stock kernel PR1.3, profilematic and inception - of course ;-)