I would like to mention that setting the blend weight to 0 is not the same as unchecking the ‘Enable’ option. The visual change might be there, but the actual actor itself is still set to ‘Enabled’ which means it still needs to be processed in memory.
Unity 5 framework is different than ours, which is why the rendering approach is different. I do understand what you are saying, but since we do not have the ability to switch our rendering option the workflow and approaches for certain features will be different.
I am sure if you wrote some code for systematically enabling and disabling the SceneCapture Actors, you could have greater control over the performance hit you are seeing. This might just be something you would want to mention on the Forums as our community is always willing to help.
Regards,