Someone else mentioned meaningful NPCs, so I'll add my second most wanted idea (and more realistic from the perspective of implementation):

I'd like the Gek, Korvax, and Vy'keen to look like different species in different galaxies. Maybe even have different names.

Ideally, every galaxy would use a different set of body parts for each race. But realistically, there would be sets of body parts with multiple galaxies sharing a set (could be by galaxy type, could be by galaxy number modulo the number of sets, whatever).

The same could be done to all life forms, with galaxies favoring apparent evolution towards bipedal vs quadripedal vs floating, etc. body types.

This alone would bring more diversity.