"If there are people who do experience a definite thing common to all enjoyable experiences, this might be one reason for the attraction, to some, of utilitarian theories -- even for taking some sort of utilitarianism to be obviously, trivially true."

People do find a definite thing common to all enjoyable experiences: they enjoy them.

Your comment raises a good point though: it would be very hard to measure one sort of enjoyment with another, especially between the "carnal pleasures" and the "intellectual pleasures", which both produce enjoyment...but how much? Without a way of measuring pleasure, you're left with subjective judgement, which may be of little use.