As you said, the help page says you can't move sub pages. I find this to be very limiting. You also can't duplicate portfolios, only sub pages.
I was going to use portfolio pages on the site I'm redoing, but I might just use blog posts instead of portfolio sub pages, because then you can put summary blocks anywhere. Blog pages seem to be more flexible. Plus I'm looking to re-use sub pages across pages, so I can use categories for that.
By the way, I love musical theatre, so I enjoyed seeing your site.