6 Black Towers and 9 Kiosks were part of my goods production before a massive makeover of my city took place. 15 of each good from the era one is in per day is great! With the recursion setup, each time I cashed in the Black Tower, a free roll of the dice was done while 3 Kiosks equaled another free roll. 6 Black Towers = 18 FP's and 60 Medals, which are good numbers. I never had a problem with Happiness despite the negative Happiness number of the Black Tower.
If the Black Tower fills a need, then use them! If not, get something else. Eventually there will be better buildings but since Black Towers and Kiosks go cheaply at the AD, consider them as useful buildings up to a certain point.