We've done multiple merrytime cruises, on both the Dream and Fantasy.
IME the gingerbread smell [typical gingerbread spices smell, so cinnamon, nutmeg, clove, possibly allspice as well...] is strongest within several feet [upto say 10-15 feet] around the the gingerbread house itself. further out from that it gradually disipates.
Various factors will influence how far away you can smell it, like time of day and how much foot traffic is going past as those affect the airflow and therefore the scent travelling...
We did not notice the scent on the deck above.
It does sometimes drift into that side of the atrium.
The house and the smell were one of our favourite parts of the cruises
We visited it often. For those who do enjoy gingerbread, the house is quite neat the explore -- many hidden things to discover if you spend the time looking [we will spend the time late at night when it is quite and few others are around, when you can stand there peering around at it and now have others wondering what the heck you are looking at
].
SW