Decoupling Capacitor Power Waste
It sounds like you already have a working board. BY FAR the easiest way to study power loss is to use a thermal imaging camera to find hot spots during operation. If the capacitors are not getting warm, they are not dissipating heat. You can now buy low cost IR attachments for your android or iPhone device. There is SEEK thermal camera and FLIR one.

Another tool that could be helpful is a high bandwidth current probe. Sometimes you can insert a wire loop in series with your component and large enough to fit through the current probe. Then you can measure AC current. The dissipation is the RMS current * RMS current * ESR.