|XP is just a number|
First, let me say that I don't necessarily disagree with you. But, I'm not talking about "design first, code later" mentality. Yes, things can be designed to death, but with the above goals in mind both while you design and while you code (which are really the same step, but that's another Meditation), you can find the balance.
The art of software (design/code/maintanence) is as much about what to leave out, what not to handle, what not to encapsulate, and what not to fix, refine or refactor, as it is about doing those things.
This, to me, falls in the category of Make it clean. Part of being clean means not doing the unneccessary.
Unnecessary security is more than just unecessary--it is a drain on resources, both when coding the program, and when using it.
There is really no such thing as "unnecessary security". It's possible that someone might do something unnecessary in the name of security. But, such things are actually not good security -- the illusion of security reduces security, as does needless complication from unnecessary measures. It's important to remember that the principles above work together -- you can't put all your eggs in making it secure if doing so would cause it not to be clean (or worse, not to work).
Designing in reusability, before there is an application for reuse, besides being a waste of effort if the code is never reused, frequently leads to design and coding descisions that only serve the purpose of the assumed reusability.
There is a big difference between designing-in reusability and coding with reusability in mind. The former, as you've said, is a bad idea unless reusability is one of your goals. However, it is a good idea to avoid practices that needlessly break reusability. Again, by using the principles of "make it work" and "make it clean", it's apparent that there are cases where reusability is less of a concern. That's why I phrased that section the way I did.
Better to code the solution to the problem at hand, and redesign/refactor for reuse
And this is a task made easier by keeping in mind potential reusability during coding. "Oh, I shouldn't make that a constant, what if I need to reuse this?" Of course, sometimes making it work precludes this -- like when performance trumps most other concerns.
"Users are evil. All users are evil. Do not trust them. Perl specifically offers the -T switch because it knows users are evil." - japhy