Round trips are just fine. Browsers are smart, servers are fast, and HTML compresses well. The site you're reading right now (HN) requires a reload. Stackoverflow requires a reload. Neither are slow to use.
If your page is really that complicated, then I suggest Vue or Preact which are efficient and designed to progressively enhance pages instead of rebuilding everything in JS.
Sites like HN and Stackoverflow have a vastly different audience than most bread-and-butter sites, and tackle different kind of issues.
If you really need a offline site then a simple service worker is all you need to cache the pages, not a big JS app.
I would like to trade out AngularJS for Vue someday, though.