Does 40k have to be rebased? Do you have any more information on this? I got a two 40k armies but have not played it on a few years, so would be nice to make certain its updated if there is changes to the system.
Is it not optional? I can't remember seeing anything offical that they need to be rebased but there is a distinct advantage to having 32mm
Yes they were changed some years ago. It might not be necessary for friendly playing, but for tournaments and such I guess it´s mandatory, as in WH 40K distances are measured from base to base
If you take a squad of 10 on 28mm and a squad of 10 on 32mm, the later has a 40mm larger footprint allowing you more control of the table so for tournaments yes your right.