I have now spent a couple of weeks using my new Acer Chromebook 11. So far I am well pleased. Battery life is as good (or better) than my Acer C720. The issue with build quality (it's not as nice as my C720) has not been an issue at all. In fact, it is nice to have a lighter laptop to carry around. My Chromebook 11 is all white and I thought it might get dirty quickly, but it has not. I have had no issues running all my favorite apps. I still think my Chromebook 11 is a tad bit faster, but it is imperceptible most of the times. I look back and see that I had my C720 for about a year and a half without any issues (in fact it still is working perfectly). I can see myself having my Chromebook 11 just as long (unless I have money to burn on a new one next year).
My recommendation? If you can get a good price on an Acer C720, pick one up. But, if you can get an Acer Chromebook 11 for less, it's a good deal.