nice post. In my experience also the lowest paying accounts are the most difficult to maintain- out of proportion certainly to the revenue they bring in. However, one thing it didn't mention here is to remember not to discount market share. In lots of apps the higher subscription plans will only be upsales- no one will jump straight into the business account, for example. And in some cases your low paying accounts are doing a lot of evangelizing for your product, or not using a competitors product, etc. Keep it balanced, for sure, but get lots of users.