I was told to build my walls so that they have a 5mm gap from the joists, then use nails every 24-48" to secure the wall.
That will help reduce sound from traveling through the joists from my basement room.
*ANY* point of contact is an avenue for sound transmission. Period. I am not sure who told you that, but if you are not going to do it correctly, save your money, and just do it "normally" and not worry about sound transmission between the lower and upper floors. It is as simple as that. You entire structure and the sound integrity is only as good as your weakest link.
Sound is vibrations, and as soon as you have a single point of contact (a nail, two walls touching at a corner, etc.), you have compromised your sound isolation.
Do yourself a favor, and go out and buy this book:
It is called:
"Home Recording Studio
Build it Like the Pros"
By Rod Gervais
Amazon Link for Rod's book
RUN out and buy this book! It will help you in more ways than I could ever describe in an internet forum!
I wonder if there's any benefit to using rubber buffers/washers between the resilient channel and the studs?
Not sure on that one, but RC is designed to be used "as is". There are other types of clips, such as the ones that Bryan pointed out, that use rubber isolation pucks.
"Never interrupt your enemy when he is making a mistake" ~Napoleon Bonaparte~