There's nothing wrong with having a Plan B. I for one encourage it. Sure it's not your dream job but it can help tie you over till Plan A is in view. I used to be a shamed of my Plan B. The more I worked there the more frustrated I got. I just wanted my dream job sooo bad that doing anything else made me ill. It wasn't until I moved to LA when I realized. I wasn't the only with a "day job" and moonlighting in the industry. I think just knowing that took a load of pressure off of me. In the industry there are no doors and in this economy there are no windows either. To make it one has to be creative. I've found that a big part of it is location. As they say "LOCATION, LOCATION, LOCATION!" There's also timing. But that's another post.
Plan B's are just as important as Plan A's. It's great to have a dream but dreams take time and money to develop. It's always best to find a Plan B that is closely related. But if it's not try to use that as a tool. Like stepping stones, use them to reach your goals. They will not only advance you in your career but also develop you as a person.