Hello,
Yes this thread is a bit old but not useless.
Network theory by itself is the ground for understanding circuits from a theoretical point of view. Not just so we can arrive at a numerical solution, but so that we can truly understand a circuit better. That's because a numerical solution is sometimes hard to correlate to a given behavior of the circuit without doing a little theory.
A good example is the series resistance in the output capacitor of a boost switching power supply circuit. You'd have to keep trying values to find out what works and what doesnt, and it may be hard to define the threshold for instability using purely numerical results (which simulators spit out).
It's always good to back up your theories with a simulation, but the simulation should not come before the theory. If you have enough theory behind you in a given field you will certainly do much better than someone without that benefit. That body of theory includes many other things besides network theory however, although network theory is at the heart of it all.