A couple of angles I like to approach these decisions from:
If you're probably going to re-invent most features of React/Vue in your project, consider using them from the start. You probably won't do it better.
If all you need is switching pages without a full reload, use PJAX.
If you have lots of static content but some highly dynamic features in some places, use React/Vue only for those features, and leave the rest to the server. Example: E-Commerce (Mostly page-based, but needs Search-Filters, Checkout etc.)
There is more than Server-Rendered vs. React/Vue. Think WebComponents, Gatsby, Rails, Phoenix.
React/Vue are useful for enforcing certain good development-practises, which may be an advantage depending on the team.
When in doubt, implement a small and well-defined feature from the project in a couple of methods/frameworks and use the experience to decide how to continue.
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