After some extensive testing, we are inclined to conclude that the only thing that determines if you get a Dream Bell Ticket is if you upload/update your island that day! Having more visitors does not seem to give you more of these tickets. If you have evidence to the contrary, please let us know in the comments below!
Get In The Mail The Following Day
Dream Bell exchange tickets will arrive the day after you update your island! At this point, check your mailbox for a letter from Luna containing the ticket. You can get one of these every day.
Uses Of Dream Bell Exchange Tickets
Sell For 5000 Bells
Dream Bell Exchange Tickets can be sold at Nook's Cranny for 5,000 Bells! This is a pretty decent price, meaning it's possible to make a not-insignificant amount of money by updating your island every day!
Other Uses Are Unknown
We are still in the process of investigating whether or not there are other uses for the Dream Bell exchange ticket. Presently we are inclined to assume that they are purely for making money, but we will continue to do research!