Ah, I've never been up Half Dome, but I used to live near the park! Between the asthma and the fear of heights, I always enjoyed it from flatter ground when I did go into Yosemite... But it's definitely a beautiful area and I'm sure you'll have a lovely time!
The stargazing up there is just intensely beautiful when there are no fires going, too-- there are just so many stars visible, it's dizzying!