The Kli Yakar suggests at some point during parshas korach, that the point of the tzitzis and mezuza exampls were that just as a begged that is completely techeilis should not need an additional string of techeilis, so too since ?? ?? ??? ???? ??????, they do not need moshe to be their spiritual leader. The same idea goes for mezuza. These ideas are very easily expressed through these two mitzvos.
Also, perhaps one should notice that the last thing mentioned in parshas shlach is the mitzvah of tzitzis and techeilis.