But these are fundamental design issues. You can't change fundamental design when you "productionize"; coming up with that design and implementing it is the development cycle.
The development cycle for me is much more about collecting requirements than coming up with a design that satisfies those requirements. That's what iterative design is about - you try something out, see if it works for the user, see what other features are really necessary for it to work for the user, and then adjust as necessary. Once you know exactly what the software should do, coming up with a design that does it is fairly easy.
My current project is nearing its 3rd complete rewrite since September, plus nearly daily changes that rip out large bits of functionality and re-do them some other way.
Fervently agree. I was one of them.
No amount of rewriting is too much - as long as you constantly have a working app.
Oh ok, you meant something quite different than I thought, and I don't disagree.
Check out arc's defmemo function. Given the ability to memoize (or cache) function invocations, changing your data structures can become simply a matter of refactoring your function boundaries and deciding which ones perform caching.