Alasdair,
I live in Greenwell Point and would obviously recommend a mooring here instead of Shoalhaven heads. There is nothing wrong with mooring a vessel at Shoalhaven heads and it is an easier drive for you from Shell Cove. The overhead power lines across the canal have now been removed and the only caution passing through there would be the ferry cables when the current is strong or the ferry is moving.
I run a Facebook community page for the local yachts called strangely enough "Greenwell Point Yachts". While there are not all that many yachts here at the moment most are owned by out of towners, Places like Dapto, Shoalhaven Heads, Canberra, Goulburn, Sydney, Nowra etc. Couple of people have moorings here and JB. I started the Facebook page so as to have a method of communicating with owners who have problems with their vessels. MSB don't give out numbers so if there is a problem it can take two days to notify the owner. The rescue association always refuses to rescue boats [they only rescue people]
The entrance in a fresh NE and a strong outgoing tide can be exciting but rarely dangerous, best to time your entry with a favourable tide.

Check out the Facebook page and scroll back through the photos and all the info you need should be there. Call me if you like or drop around.

The owners of the large concrete yacht up on the beach in the photos come from up your way. They launch a tinny at Shoalhaven heads and travel down the river to their vessel parked next to mine. Quickest way to commute.