I think you are on the right track. Actualy I know you are. 400m to 800 sprints are just about perfect for developing aerobic and anaerobic capacity. If you dont give yourself enough time to rest you'll never be able to maintain the intensity you need to achieve maximal adaptation.
If you think of it in weight lifting terms the analogy would be a ME squat day versus a high rep high intensity workout. Both will make you stronger, but we all know which will make you strongest.
Another more direct analogy we can both relate to is pond hockey versus a league game. You could play pond hockey a half hour a day for a season and you would be nowhere near as fit as the the guy who was putting in two minute shifts (or one minute shifts if the team has disipline
) for twenty minutes a game.
In my mind the most important indicator of your progress is the amount of time it takes to recover. Personaly I think a light jog between intervals until the HR gets down to 140-150 then go again is probably the best all round aerobic conditioning workouts you can do. If I had one workout to do for the rest of my life that would be it.
Workout number two is more of a GPP type which has it's place as part of a larger program but it wont be as efective as type one for the objectives you mentioned. Actually I dont think either one would build explosiveness in a meaningfull way but a few separate plyo, or o-lifting workouts should do the trick.
In bike racing you see guys all the time who train by riding super hard for about a 20 minutes to an hour. These guys never believe what they read (if they read at all), they never believe what the experienced riders tell them, and they never make it out of the lower categories. We call these guys hammerheads. It is not a term of respect.