Ahem. I found one of the major slowdowns I think. The UI layer was rendered as many transparent tiles which acted as mouse targets for recentering the map. Rather than rendering to texture, I just removed the layer's rendertree() call. The input handler uses visibility, and will nicely ignore the lack of actual rendering invisible tiles...

Release mode back up to ~360fps, with all the timer/counter profiling still enabled.

[edit: Current state, for screenshot monkeys.]