An advertiser having lots of Steem power could up vote posts that feature their products. They can target an audience based on the kind of content they up vote using their Steem power. It's similar to Google AdWords, where advertisers bid for keywords to get their ads shown next to those searches. Here, they could buy a bunch of Steem Power, then up vote posts they believe have the content and the audience they're trying to target. They can even announce what kind of posts they will up vote, giving people an inventive to produce that kind of content.
That's my argument as to what might eventually drive fundamental demand for Steems beyonds just investors and speculators. I see advertisers buying Steem in order to gain influence on the platform, if we get a critical mass of users.
RE: Steemit For Investors #2 - How Steemit Will Revolutionize Online Advertising - By Tai Zen & Leon Fu Dot Com