There's a huge number of location data aggregators out there, including Acxiom, Infogroup, Localeze, Factual, and dozens of smaller startups trying to get into the space.
They each sell their data for what I think are incredibly expensive amounts, but still far less than the cost to acquire 4sq.
They all have various amounts of trust and vetting of location data - that said, Foursquare is among the lowest in terms of trust. They've been trying to crack down hard on it for the last few years, but are still way behind the curve.
I still think a lot of the urgency behind Google+ was from Facebook throwing up a landing page for every business they could get data for. The conversations between local businesses and customers are valuable conversations to host.
The problem is that without ongoing individual check-ins the aggregate data becomes stale and useless, especially when you're talking about the kind of small businesses that are going to make up the long tail of any monetization strategy. There's no way Yahoo! would do this as a pure data play unless they have a plan to revive the individual check-ins.