Benjamin, I'd say that you'll get two contrary opinions on this one. Do the owners of the house want/need to sell during the holidays? May be some want to get rid of it quickly so they can start the new year on a different note. Or maybe they want to wait until the holidays are over. Can they afford to wait until the holidays are over? Perhaps the competition is taking the holidays off! My thoughts are I would move forward and do the mailing. This isn't an exact science. Good luck!
Im not sure about wholesalers, but agents absolutely should. Spring is when people are selling, which means the time to market is November through January.