Without a vehicle, it won't be as easy to visit Matakana, as Waiheke or Tiri. You could certainly reach the Hibiscus Coast instead, by regular bus service to Orewa.
Matakana has a shuttle service, so you could look at this possibility further if you are especially keen to see Matakana area - http://www.warkworthtaxiandminibus.co.nz/.
Thanks for the message. I have managed to get a rental car so think I might drive up tomorrow as the weather is looking good. Any beaches or wineries that you would recommend?
Matakana is gorgeous - the places I would recommend are Brick Bay winery (more platter type food than full menu but still very nice and has a great sculpture walk), Plume restaurant at Heron's Flight/Runner Duck vineyard also really nice, as is Mahurangi River winery (the latter two are probably good lunch spots). Ascension is another large winery, personally I wouldn't bother with it, in my opinion it lacks the character of the others. In Matakana village itself you should go to the Organic Blueberry icecream stall right in the village centre - such great fresh fruit icecream. There is also a nice cafe/restaurant right down on the rivers edge, walk through the movie theatre to the very bottom level to access it (can't recall the name).
Loads of great beaches nearby - Tawharanui is the most beautiful but be aware you have to drive along a gravel road to get there. Omaha is also really nice.