Computers could get 1 billion times faster and Bitcoin's hashing and elliptic curve digital signatures will still be "safe."
2^256 is a really, really big number.
2^226 is also a really, really big number. It is a billion times smaller than 2^256, but still far and away big enough.
Even 2^160 (the size of the bitcoin address hash) is big enough.
Back-of-the-envelope:
Lets say computers in a few years can do a quadrillion hashes per second-- that's about 2^50 hashes/second. How many seconds to find a SHA-256 hash collision? 2^205 seconds. That is much longer than the age of the universe.
How long to find a bitcoin address hash collision? 2^130 seconds, which is 43,161,132,283,224,056,755,882,116,619,960 years. Also much, much longer than the age of the universe.
(actually, those numbers are the MAXIMUM time. Divide by two for the average time. Insanely big divided by two is still insanely big.)
You should be worried that some weakness in SHA-256 is found that allows hashes to be cracked other than by brute-force. And if you're worried about that, then it is dumb to switch to SHA-512 now-- perhaps a flaw will be found in the entire SHA* family of hashing algorithms.