One thing I keep wondering, though, is whether “life” is tied more to the particular chemistry and environment it uses or to its patterns (the abstract information structure that can, in principle, be re-instantiated on different substrates).

If it’s the patterns that matter, do you think it’s actually impossible for those patterns to be transmitted across interstellar distances? Just like a cup of ocean water is packed with DNA, it’s at least conceivable that what we call “cosmic background noise” could, in principle, hide extremely compressed life-patterns that only an advanced civilization could recognize and reconstruct back into something we’d meaningfully call “alive.” And of course, the more efficiently you code that information, the more it statistically has to look like random noise.

Not saying this is likely -- just that if the essence of life is informational rather than chemical, "traveling" could look very different for any life that is suitably advanced.