The thing about specific needs is that they are usually narrow. You could throw darts at the dartboard of problems, working on very narrow problems for years and never get a job solving any of them. If a problem calls out to you and you won't stop until you get a job with it, then the effort could be worth it. But sometimes, even if you get THE job, you'll have a slight twist in constraints that makes most of your prep go by the wayside.