I have updated the dream town for my Animal Crossing: New Leaf town a couple of times and each time I do I get given 5,000 Bells as a reward. At first I thought it happened when you hadn't provided an update in a while, but lately I seem to get rewarded even if I upload again the next day.
Every day (once a day) you get 5,000 Bells for updating your data. Only one character per file can get this data, so... say you have two players in your town, mayor and resident. If resident updates the data on Tuesday, he/she gets the 5,000 Bells. But mayor can't get that 5,000 Bell update reward until Wednesday.
Thonky has this information (along with some other Dream Suite stuff, if you need it).