A: Yes, you should. Why? It is better to have it and not need it than to need it and not have it! Many schools are now not requiring the writing section of these entrance exams but some still do! In fact, all of the schools within the University of California public system require them. So, it is best to just take the writing section of whichever exam you are to present!
Please read this article which lists all of the schools which require the writing section of the SAT or the ACT: