I'm assuming here that cross country is your primary focus
so you're not looking to set the world on fire with the races. They're part of your cross country prep.
Just pulling dates out of the air, let's say you were going to race on May 10,17 and 24. I'd say, again, because you're not "serious" for these races, that about two weeks prior to racing I'd add some sort of faster stuff. Hills were always transitional for Lydiard so maybe in those two weeks I'd do 3 hill sessions, then maybe run a time trial at some distance that's in the range of what you'll be racing, all before beginning racing, then in the racing weeks do something like a fartlek session with kind of longer bursts, say 600-1000 meters and a second session of something faster, 200s or so and race on your third faster day.
Even if you decide not to race I'd suggest doing those kinds of runs, or something along those lines for maybe four weeks and then getting back to the distance work. It won't hurt you to do nothing but distance work between now and September but I think having a little time in there when you do some faster running will be beneficial for the reasons Arthur mentioned.
Now, if you want to go with "revised" Lydiard, as revised by Snell and you still don't want to race, have one weekly session in there with some sort of faster work. Peter told me that if he were doing it over again he'd do a weekly session of something like 10x300 or 10x400 in his base phase. You could just do some fartlek if you didn't want to get that formal. But it's all in keeping with the idea of stimulating physical systems that won't get too much stimulation from pure distance work. Oh and don't ask me what those systems are.