Well it is incredibly dangerous, but if we did make safe, super intelligent AI, it would definitely be a much greater investment than directly working on those problems.

To put it lightly, it would automate and massively bring down the cost/increase the speed of research and engineering. Sure enough money, spent on enough humans, given enough time, could eventually find a cure for any disease. But why do that when you can just ask the AI and have a cure overnight?

Of course it's not clear how safe such an AI would be (such a being could easily outsmart us and get what it wants, whatever that even is), nor how difficult it will be to create one.