While she's not sure she agrees that the Astrodome is the most important building in Houston (the thing is so UGLY!) she does acquiesce that is was the beginning of the domed stadium genre, and that makes it important! God knows Houston's developers LOVE to tear stuff down, so hopefully they can find a use for it before the wrecking ball hits it!
There are many old and new buildings that are significant in Houston, and Miss G's favorite new one has to be Williams tower, which was her trusty navigation system when she first moved here! It was a rotating beacon at the top, so she could even use it at night!
Also, props to GingerSnap Timmy- Project Row Houses made the list!