Of course, it's not ALL about metrics, and in some ways I reject the line of thinking that you can't improve what you don't measure (qualitative research/understanding can go a long way). But with quantitative research/data so easily available... it only makes sense to make use of it.
Thanks for sharing your insight!
I track a lot of metrics and keep a custom dashboard that I can look at any time to see how things are going long-term/short-term/real-time.
Not jumping on the IAP train fast enough was probably the stand-out one. Over time, it seemed like people got used to buying via IAP and almost resisted doing anything else. Sometimes it was as simple as being afraid they'd have to start over with their data if they purchased a whole different app (they wouldn't).
I think its important to let people pay when they are ready with as little friction as possible. If you have the friction of returning to the App Store, you will lose a lot of them in the process.