more mics don't necessarily mean better, often times worse. You need to know what your looking for sonically and then use the right tools.
For a strictly ambient recording, 2 channel is ideal, but 4 can really be a good thing in the right situation. 4 channel in a good room, typically I will run flanking split omnis (lower in the mix) and a main pair of cards or hypers(higher in the mix). What I typically am trying to achieve is a sense of spaciousnous with the omnis but yet still a focused and "in your face". Sometimes I use subcards as a flanking pair when I prefer some rear rejection.