Saying that we need to prepare MORE is insane. It would be like asking if Anderson Silva has prepared enough to fight a high school wrestler.
I don't think it follows that the US is prepared. Most of that money is just maintenance. You have to spend it just to keep the forces you have. You can't derive much value from the service members who have retired or the stockpiles of obsolete equipment. To put it in extreme terms, if the US stopped spending now, it might not take China very long to overtake them in capability, even though it might take decades to overtake them in spending.
The ability of the US to continue plowing money into its military is only an effective measure of US preparedness insofar as that money is used to actually, you know, prepare for stuff.