Some recent work suggests that most galaxies have too many gamma-ray bursters, such that most planets get hosed every so often, making complex life practically impossible – as if it wasn’t already. It seems that low levels of heavy elements (heavier than helium: “metallicity”) make this more likely, so that conditions were unfavorable in almost all galaxies for the first few billion years.
On the other hand, another recent paper suggests that there are many rogue stars outside of galaxies, flung there by gravitational interactions with giant black holes in galactic cores. That and spindizzies.
Seems to me that forming in a galaxy might give a solar system enough heavy elements, while being flung into the intergalactic deeps would protect you from cosmic catastrophes like gamma-ray bursts. Such stars might be good homes for complex life, especially a few billion years ago.
Interstellar travel is hard enough for us, but for these guys, it would be a bitch. That first step is a doozy.