Regardless of how we end up building quantum computers, they will be useful. The theory behind computing with qbits is well established and many interesting quantum algorithms have already been developed.

Even a 32 qbit computer would be a very serious breakthrough.

edit: by a 32 qbit computer, I mean that the device should have 32 qbits of memory in total! I'm not talking about bus size.

That is one of the cool things about quantum computing. You don't need a big device to do interesting computations.