I posted a question about who benefits from the government policy of National Parks in the United States. It was put on hold as off topic, but I want to make sure this area of scope is well defined and discussed. Are questions about the demographics of who benefits from a policy on topic?
Yes, questions about the demographics of who benefits from a policy are on topic. Questions are on topic for this site if they deal with "governments, policies, and political processes." A key part of understanding the impact of policies is understanding who benefits from them. Questions about demographics are on topic if they directly relate to a government policy.
In a democratic country, questions about the beneficiaries of policies are especially on topic, because those beneficiaries go on to vote for lawmakers. Understanding who specific policies benefit is vital to understanding the dynamics of those countries elections and how democratic forces influence lawmakers. Elections and how lawmakers pass laws are key political processes that this site helps users understand better.
Does allowing these questions open a rabbit hole of unrelated questions? I don't think so. For a question to be on topic, it must tie back to a government program or policy. "How many Americans work in factories that make auto parts?" is off topic. "How many Americans work in parts of the manufacturing sector that would be exposed to foreign competition by the Trans Pacific Partnership?" is somewhat broad, but it's a vital question for understanding the constituencies pressuring lawmakers writing the trade deal and the positions of candidates on the trade deal and thus should be on topic.
National parks are a function of the government, and I would consider questions about them and their implications to be on topic.
Keeping that in mind, your specific question might be too broad/opinion-based.
When I imagine a potential answer to that question, I imagine different metrics for "benefit", different kinds of benefits such as educational, environmental, economic, etc, and very complex ways in which a park may or may not benefit someone.
I feel as though if someone would attempt to answer that, they would need to make some assumptions about what counts as benefits, assumptions about opportunity cost, and they would need to speculate and guess.
When a question requires too much speculation and guessing to answer, I usually consider it to be opinion-based.
No, such questions are not on-topic.
Just because the answer to a question might be relevant for political decision making does not mean it is a question about politics. If we would allow such questions, then pretty much every aspect of life would be on-topic here because every aspect of life can be a topic of government regulation.
The litmus test if a question is on-topic here or not is "would a political scientist have a better answer to this question than an expert of a different specialization?". Visitor numbers of national parks are not within the area of expertise of a political scientist, so questions about that do not belong here.