The public wave UI is feeble.  No argument there.  If that were all there were to it, Google Wave would be an interesting experiment destined to fade into obscurity.  But GW is much more than that.

GW defines an underlying platform and messaging protocol that is--or at least promises to become--an important foundation for many applications.  The fact that GW is not even generally available and yet it tied with email in a recent poll for best collaboration platform suggest there is something to it.

Give GW another year or two to mature and for developers to start building on the underlying platform.  We'll see not only new and much more capable GW clients, but entirely new classes of application functionality layered on top of the GW protocol.

It's hard for me to say whether it will be important or not. Gmail was obviously good when it debuted and has only gotten better. Chrome is a similar story. And search is maybe the best example of all time.

With all of those, you could see an immediate use. With wave, I'm not sure what that use is yet.