I have a bunch of those domains. I even have keywords-keywords-keywords.com, although I don't have it up and running. I don't bother myself with SEO, as it takes a lot of time, and the search engines can change there logorithims and totally devastate your rankings overnight. There are faster and better ways to get traffic.
I buy them all the time. There are lots of gems still waiting to be regged imho. I just regged this week ; home-renos.com & air-plane.net Can't believe they were still there! Hyphens are given a bad rap (or were) by purist domainers. I for one am buying more generic hyphens based on the market demand for them.