Accelerating Galaxies.

 Within the model described, the explanation is simple: while condensation of dark matter leads to a gravity well, after the explosion as matter scatters at some point the gravitational attraction outside the expansion zone will be stronger on the forward elements of the exploded mass than the gravitation attraction by the rest of the exploding mass. At this point, these galaxies would accelerate.

"Older than Thou" Galaxies.

It we accept that a given explosion may have led to fragments causing nucleation, one particular case would be fragments being close enough for their explosions to be close and contemporary. That means that some of the galaxies will "fly" into the other expanding cosmos. If one of these "foreign" galaxies was detected after it passed the centre of the second explosion, it would seem to belong to the Universe, only its direction would be somehow wrong and, if its own explosion was older, would give an aberrant "older than thou" reading when trying to determine its age.