I’m not sure I feel a strong difference, and I am a native French speaker. “Pourvu que” might be a teeny bit less formal, something that my French teacher in high-school might have frowned upon, but that would be under “style” (the “que” sound in “pourvu que” might be harsh to some ears), IMHO. But I am not feeling the collective vs. personal nuance, personally.

For me it means the same thing as “espérons que”, it often includes other people. This is something you say to other person who likely thinks the same thing, like a parent saying to the other parent: “Pourvu que [leur fils] réussisse ses examens…“.

When you say “J’espère”, you don’t necessarily include other people, but that doesn’t mean they are likely to think otherwise. “J’espère qu’il va réussir” “Oui, moi aussi“.

However, “pourvu que” is not used much in daily conversation (neither is “espérons“), so I’d use “j’espère” almost all the time.