It doesn't matter if your + or - is before or after if the end result is still 3XP.
Two People Leave a City. One travels faster and has to stop for gas, The other travels slower but saves gas on the trip, They both arrive at the same time because of the time it took for one person to stop and buy the new gas.
And yes, Rested XP does discourage play. I had many friends who would stop grinding and doing quests when ever their rested XP ran out and then log off for the night.