Not a bad practice if you truly enjoy doing that type of thing. But if you're really doing all that stuff to prepare for a SHTF scenario though I would say you're wasting you're time, and you're a paranoid freak.
True. But we're talking about the potential difference between life and death and it doesn't take a lot of practice to learn basic survival skills that do put you ahead of 98% of other people. Even if you don't truly enjoy it there's no reason not to know some basics if/when things get nasty. Same with anything, just like you mentioned. I can hack away at php when I need to with just a little practice here and there over the last year. I'll probably never get deep into it but it's definitely worth knowing.