Hi,
the use of buffers within a bus system is always recommendable.
It is not a problem to connect two IC´s with a track of 20cm length on a pcb itself if the frequency is 12 Mc and the capacity between the naighbour tracks low.
If You wish to route via an connector and a backplane to an other board then I think a buffer is a must.
A buffered signal You may transfer via twisted pair data cable over a distance of 3 meters without any problems (12 mc).
Regards
Werner