Last year I did a weekend trip to HKG and Macau. Here is a quick run through of what I was able to see. Arrived Friday night and checked into hotel. Saturday morning up early and took star ferry to Kowloon where I went to Nathan Road and to Kowloon Park. Ferry back to HKG and grabbed the bus to Lookout Peak. Had lunch and back to the hotel for a short rest. In the afternoon I went to buy a ferry ticket to Macau and I walked around downtown and went to the Stanley Market (I am not a big shopper so I just looked around for a little bit). That night I went back to Lookout Peak to see HKG at night and I also took the star ferry to Kowloon to see the view at night.
Sunday morning - I caught the ferry to Macau checked in at the Venetian where I relaxed by the pool in the morning. In the aftenoon I went downtown and to St Pauls ruins, a fort (I probably could have skipped this) and Senado Square. There is a little bit of a shopping area between Senado Sq and St Paul's. It is small but it was packed with people and someone told me the prices were less than what you would find in HKG. That evening I went back to the resort.
Monday morning - ferry to Hong Kong.

I was really glad I did the Macau part of the trip and would highly recommend it. It is worth keeping in your plans. For me it worked to stay one night in Macau becasue it allowed me to relax a little bit after hitting HKG pretty hard the day before.

Something I found out later was I could have shown my Venetian room key and the Cotai Ferry would have been complimentary.

Hope this is helpful.