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I wouldn't bother with bluewidgetdohickies.com unless you have the time and resources to make bluewidgetdohickies.com a successful site all in itself. For example, maybe there is a niche your main site has trouble promoting. But don't buy the domain if the sole purpose is to promote bubblegum.com.
That's my opinion.
Unless each domain can "stand alone" however by virtue of uniqiue content and linking patterns in and out, dont expect them to last long in google at least. They may have some type-in (non Search engine) advantages but not really if the domain names are this long.