We have 7 full days in HK. Will it be worthwhile to go tour Guangzhou or close by for 1 or 2 days?

Yes. Generally speaking, 3 days are enough for you to visit major attractions in HK. You can use the rest of days to tour around Macau, Shenzhen or Guangzhou. Each of them contains many popular scenic areas. You can make a travel plan according to the schedule. Have a nice journey!