Ruby - we did almost exactly your trip, but in reverse (NY last) when I was just pg with DS (so our final pre-DC fling, 14 years ago).
Don't miss Hearst Castle (fantastic) Santa Barbara, Hoover Dam (scary)...we never made it to Yosemite, because even though it was late April the mountain passes were still closed due to snow. So we went to Lake Tahoe instead, and discovered the most incredible ghost town called Bodie, which turned out to be one of the most memorable places we visited. It honestly looked as if the residents had just gone on holiday, leaving everything behind.
Bryce Canyon was amazing too, but you can't drive through it anymore, and have to go through on a bus, which doesn't appeal quite as much. I remember making snow angels there (in April...).
Ah well, I'm sure I shall enjoy my week in Cornwall (sniff).