Aggregative hedonistic utilitarians are often concerned with the expected value of pleasure minus pain going forward. For instance, they may wonder how to value the expected Astronomical Waste if humanity were rendered extinct by a sudden asteroid impact.
One important consideration is that it appears that biological life as we know it generates pain or pleasure at a very low density relative to long-term technological possibilities. As Nick Bostrom's astronomical waste paper notes, the energy output of the Sun is a number of orders of magnitude higher than the energy that goes into life on Earth, and even higher than the energy going to power animal nervous systems. Further, ultra-efficient computing substrates could run emulations of animal nervous systems at much lower cost in energy.
For particular accounts of the normative importance of pain and pleasure, one could further streamline conscious software programs to have just the right features to maximize pain or pleasure produced by a given lump of mature computing hardware ("computronium").
Call computronium optimized to produce maximum pleasure per unit of energy "hedonium," and that optimized to produce maximum pain per unit of energy "dolorium," as in "hedonistic" and "dolorous." Civilizations that colonized the galaxy and expended a nontrivial portion of their resources on the production of hedonium or dolorium would have immense impact on the hedonistic utilitarian calculus. Human and other animal life on Earth (or any terraformed planets) would be negligible in the calculation of the total. Even computronium optimized for other tasks would seem to be orders of magnitude less important.
So hedonistic utilitarians could approximate the net pleasure generated in our galaxy by colonization as the expected production of hedonium, multiplied by the "hedons per joule" or "hedons per computation" of hedonium (call this H), minus the expected production of dolorium, multiplied by "dolors per joule" or "dolors per computation" (call this D).
By symmetry, my default expectation would be that H=D. Insofar as pain and pleasure involve accessibility to conscious reflection, connections to decision-making and memory, these pose like demands for both pain and pleasure. Evolutionary arguments about the distribution of pain and pleasure in the lives of animals, e.g. that in the lifecycle of some organism there are more things that it is important to avoid than to approach, are irrelevant to hedonium and dolorium. Pleasure (or pain) is set to maximum, not allocated to solve a control problem for a reproduction machine.
This is important to remember since our intuitions and experience may mislead us about the intensity of pain and pleasure which are possible. In humans, the pleasure of orgasm may be less than the pain of deadly injury, since death is a much larger loss of reproductive success than a single sex act is a gain. But there is nothing problematic about the idea of much more intense pleasures, such that their combination with great pains would be satisfying on balance.
So the situation would look good for hedonistic utilitarians of this sort: all that is needed is a moderately higher (absolute as well as relative) expected quantity of hedonium than dolorium. Even quite weak benevolence, or the personal hedonism of some agents transforming into or forking off hedonium could suffice for this purpose.
Now, the "measurement" of pain and pleasure brings in definitional and normative premises. Some may say they care more about pleasure than pain or vice versa, while others build into their "unit" of pain or pleasure a moral weighting in various tradeoffs. However, if we make use of data such as the judgments and actions of agents in choice problems, quantity of neuron-equivalents involved, and so forth, the symmetry does seem to hold. I would distinguish traditional and negative-biased hedonistic utilitarians in terms of the tradeoffs they would make between the production of hedonium and dolorium.