That sounds a lot like classic "Chinese marketing" that a lot of companies first tried when China opened up for foreign business. There are a billion people in China, so all we have to do is sign up 1% of them as paying customers and we'll be rich! Anyone can get 1% market share, right?
Of course it turns out that didn't actually work for most of the companies who tried. There has to be some kind of specific value proposition or you won't get even 1% of any market.
Typically, there are free tools, and premium tools available to those who pay. They could work on some new features, and only release them to premium users. Ideally, the features are only interesting to those that care a lot about their profile. Analytics are a good option.
If they charged people for any custom applications they wanted to put on their profiles, and then gave some of that money to the app developers, I could see both a dramatic decrease in crud, and a dramatic increase in the quality of apps in use (cause, y'know, they're paying for 'em.)