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As you noted, this is for route advertisements between sites, (including support with 3rd party devices now that everyone does VTI and IKEv2 with Universal Traffic Selectors).  You can use unnumbered VTIs and proxy off an internal interface (or loopback) and avoid subnet allocation management. You could also use the 169.254.1.0/24 subnet if you needed a numbered VTI (this is what Amazon AWS uses).

As for the "work", once you get the first one done, especially for unnumbered VTIs, you can either add more with Ansible or your own API script.  It's largely a one-and-done, copy/paste/paste/paste, implementation.  Routing policies with BGP route-maps gives you extensive control of traffic engineering.  Lots of good reasons. 😀