If you are using the setup that i proposed on my entry Enable varnish for your gears then you can change your
Varnish default configuration for prevent your cached copy being
purged, instead of this you can increase the default cache
1 week and invalidate the cache only on destructive operations. For this last part we need to patch the
Ghost engine to execute a
purge when a new post is created also when is updated.
The patch is available here Varnish purge patch as a github gist. Also thereis an example varnish configuration.