Depending on your flavor of WebEx, the cost is roughly $100/mo.
After one year you are a bit ahead with the Chromebox (~$1200/WebEx vs $1000/Chromebox) but I totally agree with your questioning of hangouts as a proven tool in an enterprise environment. Dedicated Cisco telepresence is in the magnitude of $15k to $150k depending on the feature set.
Webex is more suitable for outside sales calls or running through decks.
We've found this unit excellent for team meetings or coworking with remote team members (we were part of the pilot). The audio and video quality is very good, and unlike with Skype, the meeting is just a simple URL you follow to join; distributed in the Calendar event.
You can also bookmark named hangouts; for example if you have a 1:1 with a remote coworker every day. Or, I dunno, if you wanted to hold regular office hours - you could have essentially a static hangout that you use for an hour or two every day. Google is really trying to make Hangouts a solid videoconferencing tool, and for companies already using Google Apps, this is an incredibly valuable addition.