Maybe using one of the various spline cutting scripts on a plane and picking apart the pieces might be an option? (sorry, just woke up and not up to 100% yet ;) )
Complex splines like this can be tricky to ever get extruded. Think about all the closed inner splines where the extrusion algo has to determine which one should be capped towards the outer spline. On the other hand i was able to generate such complex extrusions in the past. Usually, the steps would involve welding all…