Be sure to make a difference between the ARexx port and the language in itself. One of the features of my Amiga that my friends are really envious of is the possibility to control most programs with a script and the possibilities to do whatever you feel like.
But, I can't say that I favour the language in itself. As soon as you have to do low level data manipulation (strings, &c), many other languages are more advantageous.
IMHO, the important thing is a solid interface to the port from the popular (and not so popular) languages.
