Crashlytics/sentry is quite useful for tracking the impact a particular error has on your overall userbase. As for the other trackers, I haven't found statistics other than DAUs/MAUs useful (and these can almost always be tracked via server-side analytics).

The Hard Problem in analytics is getting data that lets you tell real users apart from bots, when bots are motivated to present themselves as real users. Usually can't be done purely server-side.

The time decay of data is something that is rarely discussed in my view. Facebook, Google, et. al. are sitting on mountains of archaeology. Why not purge it all and adapt to a new business model where you actually generate value for other market participants and, god forbid, maybe even the consumer.