The best shape I had ever gone into a season in was when I spent the offseason on a lot of hills because of where I lived.
I was originally from midwest and went to college there. End of junior year my parents moved to Massachusetts, which is where I went back for the summer. They lived on a pretty good sized hill (centralish MA) where I had to run up at least, once usually a few times on all my runs. The rest of my run was generally other smaller hills. I sort of ignored the actual pace and just ran by feel (stopped using GPS and ran by time). Farlets and road intervals were all time based. I don't remember being concerned about the hills in training, or happy about them, they were more just a matter of fact of where I lived. Ultimately, I made by far my biggest improvement those following seasons after the hill running (both over summer and winter breaks) without otherwise changing my training except for that most of my runs were over hillier terrain rather than flat. I improved about 4 sec/mile in almost all my distances early in my following seasons.