Although I agree in longer run to grow your business properly you just need one domain and need to concentrate your efforts on just that one domain and might be better off redirect rest of domains to this one domain.
But my personal opinion is it don't harm if if you keep 2-3 main keyword rich domains too. I am not sure about others but personally I have found that keyword rich domains still tend to rank quickly and better in Google. So might be concentrate just mainly on one website but still keep other domains, might be link from them to your main domain. As sometime it might help you to RULE a particular key phrase by say getting your main website ranked number 1 and 2 and then other small one -two pages website ranked 3rd and 4th . You will end up getting 60-70% traffic for that phrase.