I do something a little bit different with my mages. I use focus for counterspelling and such (on a rotating castsequence or keyclone round-robin), "party1target" for cast assisting, and actual targeting for things like polymorph. So my macros look like:

/cast [target=party1target] scorch

rather than:

/assist SomeChar
/cast scorch

or the common

MACRO1: /focus XXX

SCORCH_MACRO: /cast [target=focus] scorch

macro pair that is pretty common.

It has some issues of its own, but it's pretty handy for classes like mages with lots of targeting needs.