Also, does anyone have experience with the earliest ones (short body). Can you fit adults in the back seat or basically just kids?
Is the 180 HP almost the same cruise but worse climb?
I own a PA-28R-180. For weight and balance reasons, I once put the petite female passenger in the front and the lanky male passenger in the back. He didn't complain about it for the 4 hours we flew like that. The copilot seat was slid halfway forward to afford him some legroom. The back seat is not useless but it is best regarded as something you have in case you occasionally need it, rather than something you plan on using frequently.
My plane has the 3-blade propeller and, other than paint, interior, and instruments, no modifications that I'm aware of since it was new 50 years ago. I flight plan to cruise at about 65% power yielding 130 KTAS and 9 gph. I usually show up on time with a little more fuel in the tanks than I planned. I recently flew a cross-country in my plane, following a 200hp Arrow with a couple of speed mods and a 2-blade prop. I think he also had a weight advantage, with less fuel in his tanks. We cruised at the exact same speed and, to within our instruments' ability to measure, the same fuel flow. He took off first, then I took off, climbed to match his altitude, and ran a little faster until I caught up with him. It didn't take that long, so he obviously didn't climb much quicker than I did, if at all.
If your mission consists of flights of less than 600 nm (that's the no-wind range of my plane at my normal cruise settings with IFR fuel reserves) with mostly (including yourself) one or two people and occasionally a third, but never a fourth adult, the old Arrow is a good plane. I am building an RV-14 because it will go faster, upside-down, and without hauling around so many empty seats that I almost never use. I will probably sell my Arrow when the RV-14 is in the air. If I hadn't lost my mind and decided to build, I would be keeping the Arrow until my mission changes to require more seats, and then the upgrade would be to something like a PA-32 or a light twin.
I would also be happy with many other airplanes, if I had found one of them instead of my Arrow. The Arrow happens to be the airplane I have now, and like all things in life, the airplane you actually have is always going to be more useful to you than one you don't. If the Arrow is appropriate for your mission, keep it in your list of planes to shop for, and when you find the right plane (panel, engine time, condition, and price) don't discriminate against it.