Basically all your points are bad! Like in very bad! For Iran nothing good will come from a declining or aging population. It means declining living standards unless there's an extreme robotization of all industries to offset demographic issues. You can replace an again population without short term migration, which is mostly unpopular. Raising nativity levels takes a least a generation, if even possible.
Sheer population is one of the definition of power and has a direct correlation to the GDP size of a country. The more people the higher the economic activity, even if they're poorer per capita in comparison to wealthier countries.
Having an aging and declining population has security implications. The more older and fewer the population the greater the difficulties in case of military conflict.
There's no benefits at all in my opinion.
wrong , first when you can't provide the food, water or job you have no business of increasing the population
when you retire the people between 45-50 then you have no business complaining about shortage of work force.
when you can't provide the level of education guaranteed in your constitution then you have no business saying the gdp will be reduce if the population reduce.
aging population is byproduct if increase in living standards and modern medicine not population not increase . what is necessary is who reach replacement threshold . population must sustainable , we don't produce enough basic necessities such as foods, water , food, electricity, education opportunities and new jobs to make our population twice in 10-15 years .
and no sheer population is not power look at how many time Arab countries get beaten by Israel , how our war with Iraq become an stalemate and .....
aging population is not security risk having a young population removing from the values that make you a nation is security risk and that happen when official get corrupts when poverty become rampart and people see the hypocrites
and sadly the gist of your post is shown in last sentence , w e need more population because rather than making our armed forces more efficient and modern we rather have more cannon fodder in case of war