Dave Addey has written a nice piece about App Store pricing. The pricing is not much of a problem with games, where Apple allows developers to make progress painfully slow unless you regularly fork over some money: Real Racing 3 is such an example.
Productivity apps should copy this model, and ask for gold for every document you create. Then give everyone one free document, and offer 5 document, 50 document, and infinite document packs as IAP options. Or for your social apps limit the amount of people you can connect to. The few apps that do not fit are either conceptually simple enough that you can make a convincing video demonstration or they live off data for which you can sell a subscription.
Interestingly Apple permits quite a bit on the App Store which I regard as clear violations of the developer agreement: in game currency violates section 2.1 of the IAP addendum (it is a prepaid account), the Perspective app violates section 2.3 as a subscription service. I suspect these are a symptom of Apple looking to allow people to make money, and hopefully will mean some official changes coming in the future.
There is also a more fundamental problem in app discovery: The App Store is so large that it is quite hard to find what you want. What you want in addition are curated stores that only carry the best software, say one for teaching science. They should not replace the main store, but be a complement, a specialist that is allowed to drop stuff it finds irrelevant, while the big store carries everything.