We have used Wagtail on a recent project of ours. We were looking for something lean which would allow us to define our pages easily and offer a clean interface to upload content to those pages. Wagtail fit this requirement perfectly. We faced some issues when upgrading to newer versions but they were expected on 0.x releases.
Pretty much our experience too. Haven't run into any upgrade issues but so far only have done a couple of minor release upgrades so might have lucked out and missed the pain points you had.