Why do you automatically assume that "no use" in this context would turn out to be a bad thing? The way I see this, if we happen to have greater intelligences working for our common good, we would be able to solve any problem better than a human could - including a possible problem of feeling useless. This would be the best-case scenario, and IMHO it would be much better than the world we have today. Possible solutions to the problem, from my limited human brain, could be bringing the human brains up to the level of the greater intelligence and hence finding new problems to solve, altering human drives so it isn't a problem any longer, abolishing AGI entirely or partially, etc. Any problem could in such a best-case scenario be solved better and faster than humans could.

I agree with you on the worst or worse-case scenario point. There are huge ethical risks and implications in creating very powerful and capable machines. This means that we need to go into this situation with our eyes open, and make sure that we discuss ethics, transparency and consequences from day one.

Enslaving humanity is a basic human drive, and I like to believe that we can do better than that if we try hard. In a pure cost-benefit analysis, it is obvious that it would be best to use such technology to help out everyone.