> It's not that my first attempt was rubbish, it's that I didn't understand the problem as well as I did the second time
I think thats too soft, I know my first attempt will be rubbish so I intend it to be so. To me the point of a prototype is to help you learn the problem more than to solve it.
If you plan to keep your prototype if it works out then I think you have missed a trick, a prototype should aim to fail quickly.
If your prototype is useful then I think it fails its point as a prototype.