mikrotik 64 bit did not an urgent or not necessary.
but when you want to install OS windows, linux, etc over mikrotik. it need more and a lot of memory.
an 64 bit for more power n stability
I thought KVM can't handle ANY sort of Windows running, but just Linux based OSes.
Regardless... x64 would indeed be nice for (Linux) VMs sake, if not for anything else.