On the other hand if you have the means to break SHA256(SHA256)) (=mining) and ECDSA (=Bitcoin private keys), why waste that on Bitcoin?
Don't get me wrong, maybe Bitcoin becomes a big threat for the establishment in the future - but there are far more valuable targets.
Another thing to consider:
Not every great cryptographer is from the USA, there are other countries with smart people out there as well... of course NSA will be ahead a bit with cryptoanalysis (I read recently an interesting article about Bitcoin mining with SAT solvers) and breaking codes just because of the ressources they have - still that doesn't mean they can magically "break" mathematics. Current crypto is considered strong enough that it makes much more sense to attack the implementation (side channel attacks) than the actual algorithm. as bitcoin however only consists of data, not hardware they need to attack the mathematics behind ECDSA and SHA256. This doesn't require a huge budget, this requires brilliant people which can show up anywhere on the globe.
Lastly:
Even though a lot of crypto nowadays is public and 100% open source still only few people understand every detail behind and even fewer then really start questioning established truths or trying out if assumptions actually hold. I bet there are some algorithms out there that are considered quite secure but that have some flaws that are very well hidden and only surface after you start from scratch and test everything. Also there's a huge class of proprietary algorithms that are "secure by obscurity" and usually easily broken because they contain rookie mistakes.
I sense that a) a good percentage of the truly brilliant minds for cryoto work are in academia, b) a lot of these folks have strong ethics and principles, and c) deep insights and results related to cryptography are a pinnacle of success in that environment. So, I have much more faith in the strength of open-source cryptographic algorithms than my native ability to analyze them otherwise allows.
I do believe that if Bitcoin failed to to cryptographic exploits, it would freeze up for a time, but be relatively quickly re-implemented with the pre-exploited block chain forming the basis for it's distribution.
I have significant questions and fears about the viability of Bitcoin, but core cryptographic attack is not really one of the reasons why.