Using something that's good and not trendy suggests intelligence. Using something that's good and trendy does not suggest anything meaningful.
That is true intelligence.
In my eyes Good and Trendy vs Good and Not Trendy is irrelevant. They are both good, so solve the problem.
Oh and "rails does not prove your smarts" should be: "Using technology X does not prove your smarts." because there will always be another X. Today its Rails, tomorrow its Open Sails, and the day after we all go back to Lisp.
My previous post only applies to the perspective of an outside observer who must guess at the reasons for a given technology choice.