Search Engine Journal has taken a deep dive into domain registration strategy, revisiting the conventional wisdom surrounding extra domain names and evaluating whether or not it requires some adjustment.
They conclude that while it’s a good idea to have common variants of a domain that your potential users might use while searching or typing in the address bar, the value of keyword-rich domains to SEO is questionable and recommends against registering several domain names for that reason alone. However, they do point out that if you have a specific project that could do well as a microsite that links back to your main site, the additional domain connections can help boost traffic. But creating such sites requires time that most webmasters do not have.
The bottom line is that while search engine algorithms are always in flux, in general, it’s a good idea to take optimization cues from their technology officers and developers for long-term SEO strategy. In the short term, register the domains you think would be most useful, but recognize that you won’t be able to register every possible domain that might potentially damage your business. You can always use the additional domains for 301 permanent redirects to your main website.