In researching Macau hotels for a potential visit during stopovers each way in HKG last year, we found the hotels in Macau to be pretty expensive on the weekends. Not that Hong Kong is way cheaper either but we decided to just daytrip over during our return leg just to save the effort of hauling luggage over. We had a similar itinerary as the OP where it was just an overnight in HKG on the way to Vietnam and two days in HKG on the way back.

It was my second time to Macau (last time over a decade ago) and my wife's first time and I'm pretty happy we visited Macau to see the sights together. We had enough daylight to see the main sights old town and taste local food while staying long enough to see the lights of nearby casinos at night. We didn't have enough time to head over to the newer casinos around Cotai though.