Learning assembly for any processor isn't bad, because despite the different instruction sets the assembler is pretty common, algorythms are pretty common and easy to port if you know what you are doing. And learning 68000 assembly, doesn't mean that you will make as much effort as in the beginning for going to PPC assembly for example. Me for example learnt mostly 6502 assembler, but it wasn't hard writing programs for Z80 and 68000. Of course having the programs written in C first helps. Read the documentations about the instruction sets and look at the instructions which will satisfy your needs when trying to implement something.
