Compared to what I hear about Comcast, I'm actually thankful for Cox but competition is always a good thing. Though in this case I wouldn't switch to Google Fiber because of Cox, I'd switch because the speeds are freaking unreal!
The problem with speeds that fast though is there isn't really a whole lot you can do with it. Unless you have multiple users or something. Most services aren't really fast enough to make that speed worthwhile. Maybe in 5 years that will be different, I'd bet more on 8-10 though.
If the price is right, then sure why not. But the most your average user will actually get out of it is looking at how fast the download speed is on a test site and MAYBE shave off a few minutes on large downloads.
Certainly wouldn't hurt to have more fiber down in the Valley though. Cox can't upgrade their old **** fast enough.