It's unlikely spying is a real rational concern for Iran,
WTF? Don't be ridiculous.
It's about the capability it provides. Can they for example deliver a nuclear warhead to Europe? They claim about 2000km, just short of Europe but that is probably a deliberate underestimate. You do not want people knowing your capabilities, you want them overconfident, underestimating you.
So if they do attack you, you can drop a conventional missile on top of Rome, and mention that the next one will be nuclear. You do not want them believing you have the capability to hit their cities knowing you have a nuclear programme in the works. That invites preemptive attack. If they know you don't have nuclear weapons that threat is ineffective and you get invaded.
It's absolutely crucial that your opponents not know your capabilities one way or another.