A LinkedIn account's sole purpose is publishing, dissemination, and advertising information about you and your company. Anything that you badly want to keep private certainly does not belong there, much like it does not belong to a large roadside billboard.

Otherwise, LinkedIn can be quite useful in searching for a job, researching a company, or getting to know potential coworkers or hires.

Email spam is, to my mind, an inevitability. You should expect waves of spam, no matter what address you use; your email provider should offer reasonable filtering of the spam. Using a unique un-guessable email address, like any security through obscurity, can only get you so far.