Spurious keys filter
Here is the problem. For a specific ciphertext, sure you could try a bunch of keys and output the couple that result in the type of plaintext you want. But what does this really get you? For a different ciphertext, likely these same keys will not result in the same type of plaintext you desire.

Recent work on honey encryption might be what you are really looking for. It is still very new, so it should not be used in a production system without understanding all the intricacies. The authors of the paper also provide some nice theoretical foundation for the area.