Better than Mars Colonization in many aspects.

Major problem: cooling and atmosphere.
Not that big a problem. At 55km the temperature is 27C (80F) and the pressure is .5 atm, similar to the pressure at the top of Denali in Alaska - easily breathable with an oxygen mask. The atmosphere is 99% CO2, which means that it can be broken down (either via a chemical reactor or via plants) to oxygen. The remaining parts of the atmosphere are nitrogen (good for breathing as well) sulfur dioxide, argon and water vapor (also useful.)

If you built a big airship that could cruise at that altitude, you'd have a very livable temperature, solar energy to run your life support system, and carbon dioxide to provide you with oxygen (and carbon.) You could even harvest water, slowly. You could inflate your airship with oxygen, which is considerably lighter than carbon dioxide.
Atmosphere problem is a lot more than pressure - it is completely unbreathable.
Every planet's atmosphere is unbreathable (except for Earth's.) However, being able to go outside with only an oxygen mask, rather than a full pressure suit, is a big benefit.

Imagine how easy it would be to explore the moon if all you needed was an oxygen mask and appropriate clothing.

In addition, since we breathe oxygen, and since CO2 contains oxygen, we have the raw materials right there.