Yup, I would do the vet thing. If it is something like asthma, you want to start treatment right away so that further lung damage doesn't occur. And also for the peace-of-mind that it isn't something more serious! In case you haven't seen it, I always recommend people with coughing cats check out this website:
http://www.felineasthma.org/moore.htm
Let me know what the results are, I'm rather curious myself.