Event Hotel will show up during short periods of time. You could check their countdown in the widget on the left side of the playing screen. You will get special managers for your permanent hotels (also for the upcoming ones) depending on your result. In-app boosters are different from the purchases in your regular hotels because they are designed for event mechanics. 
 
Even if you find hard, you will be able to reach special characters with lower percentages, but they will be useful as well. In-app boosters will obviously pave the way, but they are not necessary to get some permanent benefits for your normal hotels.