A couple things:
- For plugging wall warts into adjacent outlets without blocking, you can use (i) Dr. Ferd's Wall Wart Removers (those are the little pig-tail things referred to above), which are sold in places like Guitar Center, as well as online music stores or (ii) ordinary extension cords from the hardware store.
- Using a basic rackmount power strip has a couple benefits: it allows you to turn on stuff with a single switch (and make sure you've turned everything off) and provides some surge suppression and some minimal suppression of RFI (I think). Better units actually provide regulated power and better RF suppression, so far as I know. Some have meters! and lights!
- I think there are some products (rack mount or otherwise) that have a bunch of 9-volt (or 12-volt) lines coming out of them, which actually would replace multiple wall warts. I don't have one, though. If I did, I suspect it would probably have the wrong voltage, or provide DC when I want AC, or otherwise not work ....