Very good points, but having spent a few years in the Navy I know that is one of the issues we always worry about. My father said one of the worst things about the BRACH after the cold war ended was the fact so much was put into so few bases. This was done to save money, and the more military units assigned to a base, the more money that area will get.
So there is the political ramifications. Do you know how big Ft. Hood is?
Fort Hood - Wikipedia, the free encyclopedia
Nukes are NOT magic weapons, for a nuke to be most effect it has to be an air burst.
A 20 kiloton nuclear weapon, which would be the TOP end of a terrorist weapon, unless they managed to get their hands on a thermonuclear device, has a blast radius and damage area of: (all distances are in Kilometers)
If they got a bigger weapon, highly unlikely, but let's say a tactical nuke, top end 200kt.
As you can see, most of the base would survive, and reality check is even a strike at the heart of the base wouldn't be as catastrophic as you made out.
However an air burst might be able to achieve near that sort of devastation:
Nuclear Explosion Facts
I'm not saying these numbers are solid, after all it's a geocities link, but it's good enough for this.
It would be far easier to run a ship into Norfolk Harbor and really muck things up then to hit Ft. Hood.