In theory, the only values defensible from the first principles are 0, 1, and infinity. In practice, the difference between an hour and a week can be significant.

Will it help in the case of people actually likely to mount an attack? Not at all.

Actually, it can make the attack without scripting quite expensive, and having to write and debug a script can be an obstacle for many people. For example, I am quite tempted to make a proof-of-concept script and fire it at you just to prove my point; and I have already written scripts interacting with websites in the past; but I am still quite likely not to do it, because it would take me a few hours of work. Procrastination, trivial inconveniences, etc.

You suggestion is like prohibiting passwords consisting of a single character.

I believe that CAPTCHA would be a better analogy, because it is an amount of work that has to be done by the user manually, before they are given access to the full functionality. More specifically, it is like changing a one-character CAPTCHA into multiple characters.