Hey there Jeff,
I can speak to you as someone whose experience closely resembles your own, to offer you advice, and things to look out for.
As a sophomore, I had my best season of cross-country/track in HS. I jumped from 5:13 (1600) and 17:45 (5K) to 4:55 and 17:10. What was the difference? That summer, I went on sites like LetsRun. I breathed in Lydiard, Daniels, Coe, Malmo, everything I possibly could muster - and went out and ran a good, solid summer base. More miles I'd ever run before. I was still young so my body absorbed the new stimulus and came out stronger than ever before. With that summer base, I was able to do tick off workouts, that fall and spring, like they were nothing - it was like being on a whole other stratosphere.
Takeaway: Build that summer base.
For the next two years I languished. I never ran faster than my sophomore year in HS because I suffered a stress fracture in my shin, along with various other little injuries. Forget the injury part. I believe the main reason why I never ran faster was that I plateaued. I expected that by continuing to do the same workouts my body would naturally continue to evolve. However, your body needs change.
Takeaway: Mix it up.
I finally broke 17 my freshman year of college. The next year I opened the season with a 16:48...then improved 30 seconds in the space of 3 weeks to a 16:18. What caused it? One, I had just done a few weeks of my highest mileage (w/ doubles). Two - I always had known I was in that kind of shape. It just took "That" race, for whatever reason, to break through.
Takeaway: Have faith, and mileage is truly king.
NOW.
I was, and always have been, like yourself. I'm an idealistic person. I love plotting out my plan of attack and thinking about how, eventually, my plan will make me a whole new breed of runner - a running god. I love seeing, "60 min easy," "12x400 w/ 1:30 recovery, "prog run" etc. on my weekly schedule.
And you know what, there is nothing wrong with that. You are young. I don't know that I could do that kind of thing now because I'm (at 22 years old) not as youthfully self-regenerative as I used to be; and if I could, I would take back some of my choices, when I pushed too hard; but I truly believe that you need that experience, to push you to that final, ultimate level of what you can achieve - that is, to your potential.
I would say, first and foremost
1.) Make mileage be your most important factor. But don't try and make a number happen. Just remember, the less you pay attention to it, the more you'll be able to look back, a week after the fact, and think, "Damn! I ran that much without even thinking about it!" How easy is that?
2.) Go ahead and do a track workout if you feel like it. The most important thing about summer training is that it should be FUN. Building up a fun base that keeps you spry and excited, ready for the fall competition, is just as important as building up a base. Run the track workouts (by the way, they don't need to be on the track - go find a stretch of dirt somewhere, where you have no idea of its distance, and blast it a couple, few, several, or many times) as hard as you want, BUT - try to keep those fast workouts to just 1 a week. If you can bottle up your fire, you'll be raring to go when the season really begins.
Most importantly - relax. We runners are very fortunate in that we compete in a pure sport and so are very in tune with our bodies. That's the beauty of running. You don't have to think. You'll know if you could have gone faster a certain day, you'll know if you've just completed an epic run that was a breakthrough. Have fun with it. It's your summer and it doesn't last forever.
Good luck, my friend.
-yourshoes