Short answer is yes to both. You should visit Hong Kong AND Macau. They are very different places despite (or maybe because of) their different place in history as European colonies. They are also so close together that you can easily visit both on the same trip.
Although Macau is a often thought of as a day-trip destination, multiple days are needed to properly explore this multifaceted spot. Macau's history and culture runs deeper than its mega-casinos. Here is a 3-day itinerary for experiencing colonialism's quirkiest outpost.