#7 is a great topic to explore in its own blog post. Unfortunately, its power is undermined by obviousness of certain other points.
#5 and #6, combined, would make a great FAQ item (which would also increase the awareness among customers), and perhaps a blog post, too.
#1-#4 are the worst—they seem applicable to just about any product, including the infamous I Am Rich app.
This post, listing every justification of app's pricing, makes me wonder if the developers themselves doubt their decision.
The flimflam about updating the app just means that they don't wish to fire everyone now that they have a selling app, but instead will keep developing it with the hopes that it would sell even better.
Maybe the right reasons for stakeholders.
Not the right reasons for customers.
Paying $100 a year, let alone $100 once off, for something that improves productivity ought to be below the level of even caring to do the cost-benefit analysis.
If your employer won't let you spend $100 on a productivity tool, he's very foolish. (NB: Most employers are foolish. I've always got hemming and hawing about spending that money; can't we just do without?)