My meek understanding of how fitness works is that you build your base with miles and then on top of that you build your interval fitness with... intervals. The latter form can drop off during the offseason (or even during the season) but that's ok because you can train it back up reasonably quickly. The former, however, doesn't drop off and nothing but miles can build it. Longer, less intense, hours in the saddle seem to be ideal for these base miles (from what I've read/had people tell me).
That being said, I'd listen to the older contingent of racers/posters here. Athletes don't always make the best coaches but athletes that win consistently probably know a thing or two about training regimens that work. Will they be perfect for OP? Maybe. They're a damn good place to start, though.