I think every young child with an avalanche of 'whys' needs a scientist like Richard Feynman at their beck and call. I certainly would have put him to good use. I probably still would, now. Most of the time, I like to know why.
I have long since answered the what would your dream job be? question on various online surveys, "to hang out with kids and take all the time we need to help answer all the questions they have." Wouldn't you know it, I now find myself in that occupation 24/7. However you'll notice my dream job did NOT include cooking and laundry and baths and errands and wiping bottoms. So unfortunately Val's questions don't always get the thorough answers they so often deserve.
For some things (like when I tell her to do something) I don't always explain why, espcially if I sense it's a delay tactic. But I have incorporated an "obey first, then ask questions" rule and it's worked pretty well. I'm happy to explain to her why it is I've asked that she not stand on two stools that she's stacked precariously on top of each other, but I'd like the immediate follow-through to my command to get down, first. I'm not about to launch into an explanation as to why standing on such stools is unsafe... as if it is to be submitted for her consideration before she makes the final decision to get down or not. No. Not at all.
However, outside of those type scenarios she does ask why quite often and I do tire of answering her. I really, really try not to resort to "because" or "that's just the way it is" and though I've been tempted to follow in the footsteps of Calvin's dad for some things, I've restrained. My practice now is to keep giving her an answer as best I can and if the question is repeated, I will repeat my answer with different words or from a different perspective or add depth to it until she's satisfied and either stops asking why or makes some sort of observational comment that tells me she's happy with at least part of what I said. And of course there's always the, "why do you think that is?" which almost never fails to give me a glimpse into how her mind is working. I love that, and it helps me explain better when I see which direction she's going.
I hope to instill in my kids a love for knowledge and information, so they'll always be interested in learning, adapting and growing, as well as a love for reading, so they'll be able to research answers to questions on their own.