the dice would also fall at the same speed outside of the vaccumm.
as both are identical in size and shape they both have the same air resistance. (therefore the same terminal velocity.
a sphere of lead will fall at the same speed as a sphere of balsa wood of the same dimensions.
the wood is obviously lighter but both have the same air resistance.
if you dropped a hammer and a feather in a vaccumm they would fall at the same speed as you have removed air resistance. gravity doesn't discriminate
getting back to your original question accretion does happen on earth on a much smaller scale.
dust particles will attract each other into dust balls as the minute gravtitational force given off by the particle will attract other particles. and the pull of your house will draw them into a corner of a room (just like in space) as the mass increases other factors like friction come into play and gravity can't overcome it any more.