I've found struct fields that are pointers far more common than pointers to pointers to structs, so if nothing else it feels like *(p->target) is a more widely useful interpretation of *p->target than (*p)->target would be.
Regarding "n = -5", it would presumably be interpreted as "n=(-5)", same as today. Operators don't have spaces in them. So "n- -5" is "n-(-5)", rather than "n--5" (not valid).
As you note in your edit; we already have to watch for that pitfall :)
so really the best way out is to be as verbose as possible imo; a = a + c or auto nodep = *nodepp; nodep->next;
Compilers and compute performance have grown to make the difference negligible for code output and compilation times but they definitely take a lot of mental complexity out of such scenarios (anything helps when grokking 10k+ lines of code).
Imagine if we had to watch out for this as a common pitfall:
Even moreso, how would these two lines behave? Would they differ in semantics? Overall, -= is just so much less ambiguous.EDIT: To your point about ->, I personally think C would be better if:
parsed as: instead of: but maybe now I'm not thinking through all the parsing impliciations :)