Oz_TCH, I had the same dilemma after I bought a brand new Mercedes ML350 at the end of May. I took it home and gave it a good wash and clay. Then I sealed the paint with Duragloss 601/105 (two coats) followed with a topper of AquaWax. It looked beautiful and glistened so much (especially under lights and in the sun) that I named it "Diamond Jim". The color is called Diamond White and was a $1500 option. I think it is something like five layers of top German paint but whatever it is it is fantastic looking and will never show swirls, oxidation or anything else - as long as I treat it half way decent.
I figured that if it looks this good now just think what I could do with a machine. Since I live in Texas it would never see salt, snow or sand and it is basically a garage queen, leaving the safety of the garage only about twice a week. Since I retired I have never put over 7500 miles a year on a car and I never go off road or haul anything. So I debated about really needing a polisher. I never owned a DA polisher in the 50 years I've been driving automobiles. I've always done everything by hand but my hands are getting old and I thought a polisher might also help in the finger joint soreness department. So, I bought a Griot 6" and a bunch of pads. I tested it by cleaning out my hot tub, golf cart and shower stall and it did a great job although the golf cart was no better than I did by hand.
After everything was said and done I thought to myself that no way was this beast getting near that Mercedes paint. One false move and I've destroyed a great paint. I simply felt I did not have experience enough to work on this vehicle and did not have confidence even though I read all the books and saw all the videos. Having said all this, I decided that I will experiment further and I have my girl's older car and I also own a seven year old pick-up truck I can hone my technique with before going to the Mercedes.
The point of this story is that no, you do not "need" a DA polisher, especially for a new car. But I am certain that once I (and you) get the hang of it we will wonder how we lived without it. Even though an expert might do just as good a job as by hand on a new car, if for no other reason, a machine will make this go much easier and faster.