I think part of the problem is just that effects are pretty open-ended systems in Unity. You can implement them in many ways and whatever tools you need to edit and integrate Unity's particles and animations and Spine's animations highly depends on how that works in your game's effects system.
We could probably include a simple tool that plays a Spine animation any particle system in its hierarchy at the same time. Adding features beyond that would quickly become be too specific.
There's may be some hope for easier extensibility and integration in Unity 2017.1 when they release the Playables API/Timeline/Cinemachine. But that's still in beta.