OK, speaking of one who's actually taken dirigible flying lessons, I have a couple of points to make:
Other posters are right: propellers are just little airfoils.
The ceiling of a prop plane is a combination of three factors: thin air limiting the lift of the wings, thin air limiting the thrust of the prop, and lack of oxygen to the engine. Superchargers can help with the oxygen problem, and longer wings and/or higher airspeed will help with the lift problem, but there's not much you can do about the prop.
Airships have altitude limitations too, even worse than airplanes. Every airship contains air bladders called "ballonets" which displace some of the lifting gas. As the airship gains altitude, the ballonets are deflated to make room for the expanding lift gas. Once the ballonets are completely empty, the airship is at its maximum altitude, beyond which it can't rise without venting and losing lift gas.
Airships are *not* "extremely efficient at sending hundreds of tourists plunging to a spectacular death". The Hindenburg caught fire a hundred feet in the air, and most people on board still walked away. You can't say that about most aircraft. We think of airships as dangerous because the Hindenburg disaster happened in the relatively early days of aviation, and the disaster was broadcast live, searing it into the collective consciousness.
The Hindenburg itself was a very safe design. The disaster happened because they screwed up and used highly flammable paint on the skin. If they hadn't done that, things would be very different today.
All that said, there are a number of factors that will keep airships from ever coming back.
First, the cost of Helium is going through the roof. This is essentially what killed Airship Ventures. You could make a reasonably safe airship using hydrogen, but nobody would be willing to fly it. This might work for cargo transport, but not for passengers.
Second, they're slow. Third, they don't operate in high winds.
Flying one was one of the most seriously awesome fun things I have ever done, but I have no illusions that they'll ever be a practical means of transportation again.