Users are often unwilling to pay for apps because hardly any apps do something critical. If the app didn't exist, you could use some other app to get the job done, even if not as efficiently or elegantly. Or leave the job undone. In such a situation, it's hard for a developer to charge money.
This set me thinking: what's the other end of this spectrum? What software did I pay the most for, because it was so useful to me? The answer is Dropbox. When I first used it, it was brilliant and innovative, like nothing I ever used before. It was almost as revolutionary as the cloud. Like the cloud, it gave me access to my data everything, but it worked with files, which I already had, rather than demanding that I re-enter all my information in some kind of custom UI. Files were and still are the best way of organising some information. Google Docs, notes apps and other similar services are fine, but no substitute for files and folders, for certain use cases. With Dropbox, my files were liberated from my local hard disc, and made available on all my computers. And my phone. Edits made on one device instantly propagated to all my other devices. All my data was backed up to Dropbox servers, so even if I lost my computers and phone, my data was safe.
Dropbox was almost as revolutionary as the cloud. It solved a problem I dealt with for years with no clean solution. Dropbox was a high-quality app and service. They didn't cut corners because they can get away with it. I paid $100 for it. Per year, for multiple years. And I never felt that I wasn't getting sufficient value for what I was paying.
No other app or service was no valuable to me that I paid hundreds of dollars for it. Dropbox set a high water mark in usefulness, measured in money. That's a big achievement. Kudos.
 For just 50 GB of space, initially.