Here's some excerpts from the study:
A new study by Northwestern University researchers suggests that Mom was right when she insisted that you continue music lessons -- even after it was clear that a professional music career was not in your future.
The study, which will appear in the April issue of Nature Neuroscience, is the first to provide concrete evidence that playing a musical instrument significantly enhances the brainstem's sensitivity to speech sounds. This finding has broad implications because it applies to sound encoding skills involved not only in music but also in language.
Please read the complete post on the study here: Research Finds Musical Training Can 'Tune' the Auditory System
I think there are lot more benefits for one to play a musical instrument, even if those benefits cannot be monetarily measured. I am myself, a beneficiary of music playing. I hope to see more studies related to the benefits of musical training in the future.