The smarter companies either utilize the domains to create product related sites or minisites.
Next in line for "intelligent design" are those companies that redirect their domains to related company sites.
Next in line are those companies that at least register their brands and brand typos.
My advice: Collect domains related to your business and build minisites. Don't interlink them to start, but consider providing "text" about related issues/sites (no hotlinks).
Define value: Loyal customer? Informed customer? Educated customer? Customer awereness? Deeply informed visitor? Visitor of any kind?
The old standard applies: "It ain't the meat it's the motion."
Define the job the website is meant to perform and design accordingly.