Replacing windscreen is quite normal for some old car because of sand pitting over time, it's something you just can't avoid. When there's too much sand pitting on the screen, and the on coming traffic have their head light on, it can and will glare up your windscreen and you won't be able to see the road. Also for heater, what are you gonna do on a cold winter night and your windscreen is fogging up ??
Some of the mechanics can be way too picky I understand, but the main reason for RWC is the safety equipments on the car. If they let you go and VIC road mechanics inspect the car when you get your rego and found the car to be unroad worthy then they will go back to the mechanic and screw the mechanic who issue the RWC over.... and issue mechanics with fines and possible lose the RWC license.