You will hire smarter-than-average engineers, but with a caveat that no one talks about: they are all self-selected for being people who enjoy tinkering on computer science problems to a fault, and not necessarily your business. So the breakdown is that you get 10 super-smart people, but 9 of them are focused on myopic bits of code plumbing or reinventing APIs or something, and in practice you only have 1 smart person focused on your business.
As the other 9 continue to reinvent wheels, the nature of clojure being small relative to other open-source communities means that eventually your shiny new clojure tools get replaced by better community offerings, except you don't have the bandwidth to switch over and start using them.
Overall, velocity would be improved if you had hired 1 super smart engineer and 9 mediocre ones.
It's important to note here that while technically clojure can interoperate with java or javascript, in practice everyone expects you to use poorly-maintained clojure-ish libraries to paper over the java/javascript bits, which get out of date quickly. This effect is 10 times worse for clojurescript in the browser, although it's pretty bad for clojure targeting the JVM as well.