I think it depends on how you like to travel. I found 7 days to be a sufficient amount of time for the 4 cities I visited - was able to see the main things I wanted to see and get a lot of good food in and never felt rushed. I'm sure there are things I maybe missed in the cities I spent 1 night in and wouldn't have minded more time to explore Barcelona, but I was happy with the time I had.
I think it depends on how you like to travel. I found 7 days to be a sufficient amount of time for the 4 cities I visited - was able to see the main things I wanted to see and get a lot of good food in and never felt rushed. I'm sure there are things I maybe missed in the cities I spent 1 night in and wouldn't have minded more time to explore Barcelona, but I was happy with the time I had.