I wouldn't base my decisions on Bush's Mars initiative. When Bush is gone in 2 years (after people stop celebrating
), who knows if that will change or not? Right now the moon base and Mars have radiation problems not to mention financial problems that are not yet solved. NASA should always need high energy researchers and they do need theorists for basic science. How else will the mission people know what questions are important to ask without some good basic science? Unfortunately, NASA doesn't believe they need strong basic science and the push now is more for exploration. This belief knocks out the university funding also because NASA funds the university projects. People were guessing this whole initiative was all politics. Which NASA's are in the states of Bush's friends and relatives, Oh, Florida and Texas and that translates to Cape Canaveral and NASA Johnson which translates to exploration. When Bush is gone, the whole political landscape could change. Two years is about long enough for us to get through the basic physics classes and pass qualifiers. You can always reevaluate at that point.
I think asking if you can get a job at NASA is a perfectly reasonable question. Yes, I believe NASA hires people from all universities and the ones you mention or others on a par with them. That doesn't mean NASA will have job openings at the time. You could always do a really long postdoc at NASA, say 5 years or so. People have done that.