You are right when you say that a high torque at low / mid range rpm is important for a good driveability and a fast acceleration out of small corners, but thats because it means that you will have a lot of power in the lower rpm range.
It does not matter how much absolute torque you have. If the power output is the same (again i am not talking about max power, but power over the rpm range), there will be no difference in torque at the wheel after appropriate gearing.
A completely flat power line is not desirable. Simplified your tire can always transfer a fixed amount of torque. The transferable power increases with the revolutions. So for your lowest gear you will want a flat torque curve and a gearing ratio, so that your wheel torque is slightly higher then your transferable torque. In the next gears you will want a flat power curve, so you have the maximum power the engine can deliver, all the time.
As i said before you can of course also increase the Volumetric Efficiency (which is what a turbo does), but still, you wont be able to deliver more power/torque. It only helps to reduce the rev range to increase your engines efficiency.
You can not directly transfer some street tuning stuff to a restricted engine like in FSAE.
I don't really get your last sentence about the 600cc. A 600cc 4 cylinder engine can easily choke the restrictor, have more torque then needed (you can get almost 70 Nm) and have a large usable rev range from 5000 to 11.000 rpm.