Nailed it! This is one of the first things on my checklist for SPAs. Is it an application? Does it revolve around a single view that is not just a header tool

Nailed it! This is one of the first things on my checklist for SPAs. Is it an application? Does it revolve around a single view that is not just a header toolbar? Ok. You are now cleared for any other questions to evaluate SPAs. If the answer to either of those questions is no, just don't use a single page site. As for answering the question of how much of a primary view makes the SPA worth it. If data needs to be retained within the view while making requests, then yes. Examples - spotify, most multi column apps, ERPs etc.