Depending on your product or service, it may be a great add-on to your existing line and could encourage larger purchases. If, however, it is not complementary (which you will discover soon enough by marketing first to your existing database, either by phone, walk-in or via opt-in e-mail), you may want to explore a new brand that exists as a stand-alone.
Trying to push a new product or service to your customer base that is too far outside your current business scope does cause you to lose focus. In that case, you are better off going after a new audience under a new brand.
All the best.