I agree that quoted strings should not be the default. There is no way I want to rewrite my 7000 lines of script just to accommodate it. However, I have sometimes thought quoted strings would be advantageous.
How about a compatability mode (set to not accomodate quoted strings by default) that loads an alternative script file line parser? It could be set by the first line of a script file containing "quotes on" or some other means to identify only that file.