> At what point does customization stop being an investment into your productivity, and start stealing productivity?

The only way to get a gauge for this is practice and experience. When I first started customizing and automating things, it took forever and I was slow, and learning (and still am!). but now when I want to enhance my editor or script a task I have a handle on how long it will take and if it is worth doing, and can be honest with myself if this is really to be efficient or if I'm just looking for some fun (because it is pretty fun).