If you have enjoyed your 7-day-tour and still have time you have different options:
one more day
a) You can stay one more day in Da Lat and enjoy the city and the surrounding waterfalls.
From Nha Trang one more day
b) From Nha Trang you could continue to Mui Ne in 1 day
From Nha Trang minimum 2-3 more days
c) It is also possible to continue to Sai Gon - driving near the coast to Ta Cu Hills and Vung Tau. From Nha Trang to Saigon will take around 2 - 3 days. Always depending your wishes for more or less relaxing.
From Nha Trang minimum 6 more days
d) If you want to end your Tour in Saigon, it is also possible, to go for around 3 days to the Mekong Delta, where everything is done on the rivers.