For me, the Wakatta Workbooks were useless, besides the need to use them for listening exercises (which I just looked over to a friend's book whenever we did them). I didn't buy the workbook but if I did, I probably would've also used them for the reading comprehensions.
Wakatta is good in that it gives a pretty good explanation of grammatical structures, and provides a list of vocabulary to learn with the chapter's theme. It contains all the grammar you really need for Continuers, but if you want to learn more, I suggest you get a grammar dictionary.
I have 'A Dictionary of Basic Japanese Grammar' which contains all HSC Grammar and alot more. It has clear explanations of grammar, providing sample sentences, notes explaining when and when not to used them, special rules etc. They are around $60 but if you're willing to fork out the money, it is a good investment for learning Japanese during (and beyond) school.
For textbooks, grammar and vocab are roughly going to be the same. The only thing different would be the reading passages and the listening exercises.