Some law review competitions involve both a writing assignment and a bluebooking/cite-checking/editing test. Others give you just a writing assignment, but give considerable weight to the bluebooking and proofreading of the paper. Generally the substance, the organization, and the writing style are given more weight than the more technical bluebooking, cite-checking, and proofreading. But the latter are often given a good deal of weight, too, and for good reason: Bluebooking, cite-checking, and proofreading will be a huge part of your job as a law review editor, and the law review is naturally looking for people who are good at that, and (more broadly) who are careful, meticulous, and hard-working.

But here's the twist: The substantive evaluation of your paper will inherently be subjective. You might have a great argument, but if the readers take a different view, they may not evaluate it as positively as they should. That's true for professors -- the grading of essay exams is often quite subjective (not by any means random, but subjective). And it's even more true for law review write-on grading, given that the essays are usually split among different teams of several readers, so that different essays are graded by different people.

On the other hand, what bluebooking, cite-checking, and proofreading errors you caught (or made) is more objective. If you do really well on this, then you can insulate yourself considerably from the vagaries of the more subjective grading of the substance.

So if you think you can be good at the technical stuff -- if you have a careful eye and a meticulous temperament, and can catch most errors if you have the time (and if you've familiarized yourself with the Bluebook) -- then invest some time into the technical part of the test.

Naturally, you should still not bomb the substantive part, so don't let your bluebooking completely distract you from your writing. But if you think you can be good at bluebooking, work hard at it. That way, even if the readers are for their own idiosyncratic reasons not wowed by your substance (brilliant substance, of course, but brilliance so often goes unappreciated!), they will be wowed by your objectively great performance on the technical portion.