Is cross country going to be a waste of my time as a sprinter on my off season?

This question is often asked with the misconception that running distance somehow hurts sprinting. From personal experience after training for several iron distance events at the age of 45 (workouts consist primarily zone 2 and seldom go above zone 3), I can still manage a 00:55 400M. That is one second slower than my old high school varsity time.

.... Unless you are a specialized ELITE runner specifically training for Nationals or elite events with a private coach or at the Olympic training center, XC will most certainly lead to improvements in your recovery, durability and endurance base for the 400M.

XC improves your LT (Lactate threshold) and helps build zone 4 / Muscular / Anaerobic endurance.

Because you run on different terrain for longer periods, your leg muscles and nervous system are conditioned to "stabilize" better and you are able to maintain good form for a longer duration.

As the 400M or shorter are essentially "fast twitch" events, your body will start to engage both fast and slow twitch for the shorter races -- more muscle mass engaged = faster running.

You may also wish to incorporate strength or HIT training which include lunges / jumps / squats etc. to improve quad strength.

Yes, cross country will most likely hurt you for sprinting (if you attempt to do good). Jogging or running train and create slow twitch muscle fibers, while sprinting trains and creates fast twitch. I'm sure you know all about the difference so I'm not going to explain it. But there is no point in training your muscles to be fast twitch in the spring, just to re-train them to be slow twitch in the fall. You are not going to really gain better results as in the 2 types of races are completely differint. I suggest football or soccer as a sport to help you keep Your fast twitch muscles.

if you run the 100 and 200 I would not recommend you run cross country.

You can do other work more suited to sprinting in the fall.

It won't give you more footspeed, but it will keep you in shape and you'll be ready for the track season .

This question is worth more attention

No, it will improve your stamina-which will improve your sprinting (: