For all I can tell (and I've been on a hiring committee for the last 2 years), to have extra areas of expertise is always a plus, and to have areas of expertise that can connect you to other departments is a great plus. The caveat is that you still have to do something really good in at least one area. Having just mediocre record in many areas won't work.
Now, if somebody really doesn't want you to be hired, he can claim that you have "lack of focus" but you can be 100% sure that if you were working in just one area, he would claim that you are a "too narrow specialist", if you were married, he would claim that "you are too busy with family to do good research and won't come anyway because of a two-body problem", if you were single, he would claim that "you don't have any ties and will leave as soon as you find a girlfriend somewhere", etc. I'm exaggerating a bit, but the point is that one first decides whom he wants and whom he doesn't in some often fairly mysterious way and then puts forward logical arguments to convince other people. If that one is as ridiculous as I was in my last two examples, it is obvious to everybody but if he is seemingly (but only seemingly) less ridiculous like in my first two examples, that may fly and if a job candidate hears of such stories, it may make his head spin.
Just make sure you have a good research record and a fair teaching one and let all other things sort out by themselves. In many places the hiring process is more "political" than "scientific", so you can easily get or not get hired because last year group A quarreled with group B and now group C uses this feud to dominate the hiring. What arguments will be aired during the discussion in such case won't matter in the slightest.
Don't assume that when somebody says something, he really means it, and rely on your common sense more than on various rumors. You do not mind if the plumber you called to fix your sink is also a well-known singer in the local choir as long as the sink is fixed right, do you? Moreover, if you sing yourself and he has time for a chat, you may have a good conversation with him in addition to the service. But, of course, if you don't care about singing, you'll just check that the sink is OK in the end of his visit.
Similarly, working in area Y won't diminish your credentials in area X but you shouldn't expect the "X-only" people to appreciate or even to care about your "Y-achievements" without an external prompt. If there is someone in the department who understands Y, he'll attract their attention to it. But if there is none, just consider your Y-knowledge as an ability to speak Chinese in addition to English when visiting some rural Southern area. Nobody will admire it but nobody will consider it a drawback either unless you start to demonstrate it to everyone and insist that they appreciate your language skills.