Incorrect. Rested experience only affects the killings of NPCs, double XP as a part of this promotion affects literally everything (space, quest rewards, PvP, etc). Technically, this double XP is way better than what you would normally get from rested.
Then, as I listed above you can increase those benefits through boosts and Legacy perks.
Ah, I wasn't aware that the rested bonus only applied to killing mobs. Thanks for the clarification.