Definitely yes.
We stayed at Poly in early Dec, and we made a breakfast reservation for Kona at 6 months out. I'm a "constant checker" on the WDW site and most of the Kona breakfast and dinner spots were full at about 3 months out. If you typed in 10am, the closest you'd get would be lunch. And at dinner, you could get a spot really late maybe around 9pm. Available yes, but not great times. And, on top of that, we waited 45 minutes to be sat after we checked in at the podium because they were so busy. We checked in at 9:55am for a 10 am reservation on Friday Dec 9th and were sat at 10:40am. But, the food was so good it was totally worth it! And our server knew how long we waited so she got us fed and out the door in less than 30 minutes!
So, yes, make a reservation. And be mentally prepared to wait. We waited 30 to 40 minutes for O'hana breakfast and dinner reservations on that same trip too, so it seems like it's a "Poly thing"!! Or, more probably, our bad luck!!