I have some concerns over that too, but ingress is completely independent, which means, if they really don't see it fitting into their strategy they can either spin it off of sell it to another company, hopefully.
Yes Google reader is somewhat independent too, but at least it has "Google" in its name. They can't spin it off of sell it.
Did Google ever sell some business?
I would say yes if that includes departments of companies they acquired.
During the IO stream yesterday, they talked a good deal about Ingress. I think you are safe for now. You may even want to check in on some of their current IO promotions.
Is it fun?
Depends on your personality. If you enjoy stuff like Geocaching, it would probably be fun, but if you live in an area with a limited amount of portals or don't like travelling outside your regular area, not so much.