You need to get Joe Friel's "The Cyclists Training Bible." This man has worked with a number of top cyclists and knows how to get top performance. To give you a brief answer, most cyclists rely on periodization of their training. Lance Armstong is perhaps the most well known advocate of this type of training. He focused his entire year of training so that he would peak for the Tour de France. If he performed in any other races, his intention was not necessarily to win, but to advance his fitness level. Periodization breaks the training year into blocks. In the early blocks your work outs are of increasingly longer duration but low intensity to build aerobic conditioning. (This would be the time when you are taking 6 and 7 hour rides.) As you progress through each block, workouts become progressivly more intense to build muscle strength. (This is when you start doing
intervals ad nauseum.) When you peak, everything becomes easy, except you are expected to kick a** and take numbers during races. After your peak period, you go back to developing aerobic fitness...
To put periodization to work, you look at your cycling year and decide what few week timeframe contains your
most important events. Then lay out your training schedule so fitness is at a peak at that time. If you'll read this book, or check out any number of other coaching systems, you see they all operate on similar principals.