"Optimistic" SciFi seems quite personal to the reader. Where one finds M Banks' Culture series optimistic others find it highly dystopian.
I personally find the most uplifting books the ones that are the most "dystopian" such as Anthem by Ayn Rand and 1984 where the underlying message is about hope and our humanity.
I personally find the most uplifting books the ones that are the most "dystopian" such as Anthem by Ayn Rand and 1984 where the underlying message is about hope and our humanity.