I have thought about the multiple domain strategy. I see it as more of a diversification strategy than spam.
I know of one company who was ranking first for a group of good keywords and they built a great business around it. After a few years they were doing really well and had multiple warehouses and lots of staff. Now after the latest update google has decided that they don't like their site and have dropped it to the bottom of the first page. Within a week there sales dropped 75% yet they still have all these overheads. Really bad for business.
If you have multiple domains and you use different SEO strategies for each of them there is less chance of you loosing all your business/traffic in one hit. Don't put all your eggs in one basket.