The low temperature low energy devices would be more akin to crazy deep extremophile lithotrophic bacteria or deep sea fish on Earth, living slow metabolisms and at low densities and matter/energy fluxes,

Hmm I think you misunderstood my model. At the limits of computation, you approach the maximal computational density - the maximum computational capacity per unit mass - only at zero temperature. The stuff you are talking about - anything that operates at any non-zero temp - has infinitely less compute capability than the zero-temp stuff.

So your model and analogy is off - the low temp devices are like gods - incomprehensibly faster and more powerful, and bio life and warm tech is like plants, bacteria, or perhaps rocks - not even comparable, not even in the same basic category of 'thing'.

In any situation other than perfect coordination, that which replicates itself more rapidly becomes more common.

Of course. But it depends on what the best way to replicate is. If new universe creation is feasible (and it appears to be, from what we know of physics), then civs advance rather quickly to post-singularity godhood and start creating new universes. Among other things, this allows exponential growth/replication which is vastly superior to puny polynomial growth you can get by physical interstellar colonization. (it also probably allows for true immortality, and perhaps actual magic - altering physics) And even if that tech is hard/expensive, colonization does not entail anything big, hot, or dumb. Realistic colonization would simply result in many small, compact, cold civ objects. Also see the other thread.