They were used to be pretty rural and few people visited.
Ximendin is for teenager but I did notice the last few years there are cheap but nice hotels available. I will try the next time I visited. It used to have a lot of little girls there looking for older men to sell sex but it seems gone now. There were also quite a few prostitute locations before and they are gone now. The more modern part of Taipei is in the east but area like Ximendin does have its charm and adventure.