I think solo artists and groups are very different. It would be better to compare to Fifth Harmony or even better One Direction. Boy groups have it better because they can appeal to all age girls. Girl groups can either be cute and appeal to smaller girls, or sexy and appeal to an older audience. This is because, unlike Japan, girls can like boy groups but it's a little odd for guys to like girl groups unless they are hot and sexy. At least in USA, I've never heard of a guy saying that he likes a group because the girls were cute. But I've heard many different age groups with girls saying that they like One Direction.
Having bonuses for fans who buy the groups single/album/ect. are a more new concept. When H!P was in the Golden Age, they never really had this (if they did please correct me). The earliest fanclub event was in Hawaii in 2005. It was really AKB that brought this new thing of a benefit of buying the physical copy. That's one of their things is the new thing where you can see your idol up close and personal. Unfortunately, this albums are more often then not discarded. After one of the Senbatsu Election, there was a picture of all these used singles in the trash.
And American singers do their own bit of pandering to their fans. Ever heard of backstage passes? Crazy expensive tickets to hang out with your favorite singer. They even release their concerts on DVD. But I don't think idols will ever reach the popularity of Selena or Ariana. Not saying they aren't good, but the language barrier is such a hard one to cross for a large majority. Other then songs here and there, the only songs that make it big in America from overseas is from England. It's stupid and I wish people would have more of an open mind. The closest H!P got to having an idol solo artist that was big was Aya Matsuura.