to emphasize how complex a question like this is, let me give an example.
Piet Mondrian is an artist who made vibrant paintings of large square blocks of colour. I personally find them incredibly beautiful, though this is unimportant.
There are experimental tasks that researchers can do in order to occupy a person's attention. This is actually not all that hard. Say you have a display of red C's and green Os, like 10 of each. Then, there is a target, a red O (the idea being that you must attend to both the colour and the shape of the object in order to find the target, and it occupies your visual system, because it can't find the target by only looking for red things or O shaped things, it has to mix the info together).
So, here is the task. Subjects look through the search display of Os and Cs for the red O target. as they do this, a Mondrian-esque picture is displayed below the search display.
After finding the target in a number of searches, subjects are shown various mondrian-esque pictures, which they have to give a subjective evaluation of. By selecting abstract colour based pictures, it reduces the chance that a subject will remember an exact piece shown during the display (obviously display pictures were randomized, lest one thinks only the less beautiful ones were presented, and yes, there is a chance that, for each observer, the pictures displayed would have been subjectively less beautiful, though with statistical analysis [and considering the paper was published in peer review] the probability of this is far less than of the conclusions I'm discussing).
Subjects would rank the pictures that had been present during the search as less beautiful and inspiring than those that had not been. This shows that an emotional response to stimuli is based largely on the context that stimuli was presented in.
So, with relation to this thread, defining what constitutes and emotion or emotional power is going to be a difficult hurdle to begin with. Adding the fact that attentional prioritization and immediate context have an affect on emotional processing gives yet another layer of complexity to the issue.