I'm doing a web game startup with one other person, and I'm considering attending GDC for the first time, but we're really tight for cash.
We support ourselves with contract programming. Any money we spend on passes and plane tickets results in us having to do more work for other people, slowing the growth of our startup.
Some people say that GDC is a good way to meet clients, but fortunately we have plenty of client interest, so I don't consider that a major concern.
Still, it's generally good to network, and it's healthy for us as designers and developers to learn from the rest of the community.