I don't have much knowledge in this domain. But it might be worth firing dud rockets if they cost lesser than the actual ones.

If you can fire 10 rockets in the same cost as 1 genuine rocket. Then essentially the enemy can drag you into a war of attrition.

A dud would cost the same - the warhead is the cheapest part of the rocket.

Rockets without a payload are lighter and have greater range so you can attack more northerly targets - for example Tel Aviv. They are about public relations far more than they are conventional military weapons.