Neh, size doesn't really matter as long as you have fun! (Wife on the right, kids of friends of ours on the left.)
But, when it comes to old "pop-pop" boats, size does matter! Well.. ok, that's also not true. But, I convinced my wife succesfully that our previous (easy set) pool was too small for my boats. (If I could have it my own way, I would start digging up the garden. But as usual my wife is right, for about two months of warm weather a year it's isn't worth the effort. )
(Boat in picture was made by Gobar in Indiana, the USA in the late twenties. Unfortunately, the engine needs repairs.)
For those who happen to like old tin toy boats as much as I do, here are my videos of some of them sailing:
I think I am the first one showing a standard Intex pool, too bad really. I have seen some great pools on Youtube with woodworking to hide the liner etc.