The visual approach one has to be read back - it's been added to the AIP readback requirements list:
"e. any approach clearance"
I usually read the leave control area on descent back just on the basis that the only reason they haven't given you a specific altitude is that you're leaving controlled airspace. You are still changing levels within controlled airspace to achieve that, and as such the need for a read back is the same as any other altitude change. It's definitely a grey area tho.