1st, get Friel's book. Overtraining is defined differently from your definition: it's a physical state, normally a state of exhaustion from too much work load. Most people never get there as it requires mental fortitude to ignore the troubling signs (reduced performance, high HR resting, low HR exercising, fatigue, susceptibility to infections) and keep on at it. Most probably have experienced symptoms of overreaching
2nd, for most, riding more is the way to become a better cyclist. Cut the weights to 1-2 times/week unless you are a track sprinter. Circuits are fine. I normally do 3 sets of 25 reps in the winter.
3rd, you need a good base (4-5 weeks of easy riding at high volume at low intensity) before you do intensity. If you don't have time, you should at least do something like one long ride and 2-3 sweetspot (high right below lactic threshold effort) efforts before doing VO2 max and the such. Check the workout recipe thread in the racing subforum. Do note that for people who do sweetspot training rather than a load of base, many already have a very good foundation and have adapted to the physiological needs of cycling over many years. Alas, they can get away with not as much zone 2/base miles. This is less the case for beginners
4th. You do extra hard efforts in order to peak. After doing a month or so of really hard (say VO2 max level efforts), you'll plateau, and eventually see your performance drop. Trying to hold the form during the plateau is one of the ways to ensure overreaching. In case i didn't make this clear enough: you can't hold your top form year around. Now, your best form next year can definitely be better than your best form from this year if you train correctly, but that top form can't be held because your form as a function of time is periodic.