I would probably spend more time thinking about what it means to be a smart professor than what it means to be a smart graduate student. You are not a graduate student anymore. You might have been much less talented as a student, but could be much more talented as an advisor.
In the normal working world, project managers often stay as project managers and workers stay as workers. This is because being a manager is often just a totally different skill set, and usually needs more soft skills and less technical ability. Hiring the most talented worker to be the boss is often considered to be a poor choice in general.
In my experience, the skillsets for success in graduate school is completely different than success as a professor. So much so that that I would usually put my money betting on the success of a less typically successful graduate student in their performance as an advisor.
Grad student success is mostly hard work and a little bit of talent and luck. I've seen a lot of professors who when they were students were really technically talented but we're really just following the orders of their advisor. They get a lot of papers as a student, and then we're totally clueless about coming up with their own ideas and direction. Usually they just try to do research in exactly what they did as a graduate student with one or two extra complications.
Professor success is I think more flexible. Being a good boss and high charisma with no technical talent is a very viable strategy, and is often the most successful (I've seen this mostly in experimental groups but also sometimes for theorists). High technical ability professors can also be successful but usually have much smaller groups as the professor is often less able to offload the work, since he's the true talent.
Also, big picture understanding and gut feelings are much more important at a higher level in my opinion.
If you're particularly worried about your technical ability, just try to collaborate with some professors that can help out in the ways you can't. You can have your students go visit other professors and go on lots of conferences. (And in the end your work is sort of managing this web of connections.)