I've been dreaming up what I would consider to be an "ideal" sentient being and there have been a variety of fantastic responses to some of my other questions that got me re-examining my design.

First, let me give you a very brief description:

Reptilian/avian in basic external and internal biological structure.   

About the size of an armadillo, stands upright with a tail for support and balance, opposable thumbs, three other fingers. And, much like an armadillo it would have an exterior shell, however more like a segmented turtle shell that it can escape into.   

Cuttlefish-like eyes that allow for seeing polarized light.  

Densely packed neural clusters in the brain like parrots, so in an animal the size as described above, about the same intelligence as a human.. just much older.   

Naturally occurring anti-freeze agent in the blood stream, much like the leopard frog, and the ability to slow down their metabolism like a painted turtle to a point of using almost no oxygen for long periods of time (months, potentially longer). 

Anyway, all of these things could potentially come about naturally in the right kind of environment (long periods of darkness/cold followed by long periods of light/heat, unsophisticated predators, etc,).

My problem is, at what point of an intelligent species evolution do the rigors of the terrestrial living no longer apply and begin to revert?

Take humans for example. We are relatively hairless, have very poor teeth for killing prey, etc. We have hands to catch food with, and can build shelters so we are by and large weak compared to other animals that still rely on their speed/camo/shells/eyesight/etc. to survive.

Could my invented species exists in the form described, or is it more likely that due to the time and evolution of their species after mastering the use of their hands they would begin to devolve?