jenn-I think it gets to a point where you can just run 13 miles no matter what-no matter what a written plan says you "should" do or not. I kind of just think, "either I can run it or I can't" once you get to the place you have run several regular half marathons. You just finished one, you have more coming up--don't get stuck in a rote schedule of following what I or a book or a "maintenance" plan says. That is the freedom of getting your body up to a certain mileage of running. Just run, go long 1 day a week. Run fast 1 day a week. The other days just run-don't run less than 5 miles if you can do the time (except the fast day). Lift some heavy stuff 1 or 2 times a week. We run longer than primally suggested but I think it is "in" some people to just go and keep going.
Mentally I try not to even let 13 miles register with me. I don't even think about my body or what I am doing for 6 miles-I don't look at clocks or try to maintain a speed or anything--just run free 6-9 I work and engage to keep on what I have been doing. 10-13. I count down the miles, evaluate some aches and pains, etc. When I run more than that I really have to keep off the clock or I will get frustrated at myself for speed and things.