A little experiment for sake of illustration, before I outline the details of the Whirly Bird: Take a 12-inch ruler, preferably the thin wooden variety that schoolkids use. Hold it on its long edges between your thumb and your remaining four fingers. Now, holding your hand in front of you at waist-level,
palm up, throw the ruler upward and forward, letting it roll forward off your four fingers so that it spins about its long axis, similar to throwing a softball underhand and making it spin forward. Confused yet?
If you did this right, the ruler should not just fly up and fall down like a rock, but it should actually go in a tight arc, first up, and then curving rapidly toward the ground. This is due to the spin.
So, Whirly Bird idea: Instead of an airplane with fixed wings, which is limited in how slow it can go, or a helicopter with wings which spin around the middle of their length, the Whirly Bird has wings which stick out to the sides (similar to a conventional airplane), but rotate about their longitudinal axis. You've already seen how a spinning ruler heads straight for the ground when going forward with a forward spin, so to generate lift and avoid that downward tendency, the Whirly Bird's wings will rotate backwards. Note that there will be a traditional engine and propeller in front of the aircraft to pull it forward. Additionally, the spin of the wings may be powered at first, a la modern gyroplanes, which spin up their wings on takeoff to generate more lift. Also, for higher speeds, the wings may be stopped in a horizontal position, like a traditional airplane.
Positive benefits: Low flying speed, probably highly stable, built-in parachute (autorotation, actually).
Note: I know this is baked on a micro-scale, in the form of a kite-esque whirly-bird plane thingy. It, however, is not powered, must remain attached to a kite string to stay aloft, and is too small for my big toe, let alone any passengers.