How big is your dining party?  In my experience, this far out, you stand a very good chance of getting a dinner ADR, especially if you are a party of 4 or less.  Persistence is key.  Check whenever you have the chance.  I've always managed to get an ADR, even for last minute trips.  The only time I couldn't get dinner was for a party of seven two days after Christmas a year after BOG opened.  We had lunch instead. It's honestly easier to get BOG after 180 than it is to get Ohana. 
I do think dinner is more special than lunch, more "formal", as dining in a castle should be!  Plus the beast is there.  Since I've been there quite a bit now, my preference has switched from dinner to ppo breakfast.  But for a first timer, dinner is essential, I think.