An alternative to a straight 7x Exp event is I think what they did on Nost -- increase the rested XP generation rate, and extend rested XP to 4 levels instead of 2. 
  
So, allow players, when camped out of the game, to generate rested experience twice as fast as normal, and allow rested experience to build up for a total of 4 levels, instead of 2. 
This will encourage not only new players, but also will get some current players more interested in leveling alts, which will help increase the 1-50 population.