Thanks OS4, I guess that all makes sense.
However, on my ten milers, I'm already pretty comfortable running 55-56 minutes on measured courses. I have broken 55 but that was one of those magical days where it's just effortless to run. Oftentimes, after a 56 minute ten miler, I don't even feel like I need an easy day. That part of training definitely comes very easy to me. Oddly enough, though, I am a very poor cross country runner despite the ease at which endurance work comes.
I'll try to add in your suggestions and will make note of any progress (however, I have an excellent coach who I love working with, and he might be hesitant about taking suggestions from the internet. However, he is convinced I am a 5000 meter runner and that there is no need to do so much work for events that are not my primary event- he thinks 200 and 400 times are largely fixed, and that if I haven't improved them with hard ten milers, they won't improve).
If I could get down to 50.x and 1:51, that would be fantastic for me- I know that with my endurance, that would set me up for a sub-4 mile. The week before I ran 3:52, I ran a 1:56.9 800 and was delighted, because I knew that, for me, going through six seconds slower than that in a 1500 would feel effortless to me.