My argument for SPAs rests on the completely subjective yet I feel incredibly powerful impact of latency. When anything takes more than 50ms to react, it becomes mentally jarring to the user. Whether it is typing in an SSH session, clicking a menu with a mouse, auto-completing a box, etc - all these things generate a completely different human response and relationship with the application if they get below that thre…
It's incredibly wasteful to do a SPA for one autocomplete field, or one map widget, etc. HTML delivered directly to the browser is very responsive.