The steam from a vaporizer can loosen mucus, especially if the mucus has become thick. (You can get a similar effect by draping a towel over your head and bending over a pot of boiled water; just be careful not to burn yourself.)
A humidifier will add moisture to your immediate environment, which may make you feel more comfortable and will keep your nasal tissues moist. That's helpful because dry nasal membranes provide poor protection against viral invasion.
Dry nasal passages are prime breeding grounds for the cold virus. Although doctors typically recommend saline nose drops during the winter to keep nasal passages moist, a recent study compared saline drops to sesame oil. The people who used sesame oil had an 80 percent improvement in their nasal dryness while the people who used traditional saline drops had a 30 percent improvement. While it may not be a good idea to shoot sesame oil up your nose (it could get into the lungs), try rubbing a drop around the inside of your nostrils.