Just to add a small anecdote, I have no involvement on the design side of the house but there isn't a rocket that leaves Hawthorne without touching my hands at some point, and I've always been impressed with Musk and some of the other more senior engineers, Tom Mueller deserves to be called out in particular, for how much they know about the low level technical things that go on here. I'm very, very, very low on the hierarchy here but I've escalated things to Musk and other VP's in the past when I felt it was necessary and they always took the time to respond to me.
Also, and this was particularly true when we where in much more cramped quarters on the production side, I would run in Musk on occasion in my area and he knew way more about the intricacies of my work, and the equipment I was using, or complaining about, than I would have assumed considering all the things he's responsible for.