I've only ever worn high heels once ... and let's not go into that! ... so, I can make no personal comment on the value of this. However, it does seem very logical.
According to this article over at Core77, Marte den Hollander, a recent graduate of the Faculty of Industrial Design at Delft University of Technology in The Netherlands, has designed a pair of ladies shoes which are convertible between high and low heels.
The site also alerted me to the existence of the Virtual Shoe Museum. Good thing it was a rainy day :-).