I don't get the feeling that a superior intelligence is going to be so petty as to just waltz around the universe sucking up resources.

Sucking up resources? Nobody else is using them. They're just being wasted; hastening the heat death. One star will only last billions of years. All the matter in a galaxy could be organized to support a larger civilization for much, much longer.

After all, any post-Singularity Society should realize that the ultimate goal of their intelligence is to merge with the rest of the universe.

You are making a claim about a very large portion of possible minds. Also, I don't even know what you mean by "merge with the rest of the universe."

Why would that mean that they must eliminate all other intelligences along the way, rather than using those intelligences as a proxy to complete the task of total utilization of the universe's energy.

First, aliens that evolved separately wouldn't have similar values. Some of them would actually be threats if they valued paperclips above your civilization. Second, automated probes can do a much better job of organizing matter than some random apes with nukes.

My point is that we do not yet know enough to even begin speculating on possible motivations for ET, until such a time as we can sort of terrestrial motivations among our respective intelligent species.

Actually, yes, we do know enough to speculate. We notice that everywhere we look, there is no evidence of alien intelligences. The lights are on but nobody's home. So there are three possibilities:

• Every civilization that has ever come into existence destroys itself.

• Every civilization that has ever come into existence "transcends" in such a way to make the universe indistinguishable from ordinary stars and galaxies.

• There aren't any other civilizations in our observable universe.