People who say we don't need Gigabit Internet are missing the bigger picture. Content will continue to evolve, and the consumption of content is going to grow.
We need to be forward thinking with our infrastructure in order to accommodate and facilitate that evolution. If we continuously stay mired in the idea that, "aww... this is good enough," then we will never progress. It won't be just about watching 4K streaming movies either. Eventually, the Internet will need to support much more advanced concepts like fully-HD, real-time video teleconferencing and other forms of long-distance instant communication.
Finally, our PCs have become so fast that the Internet (at current average speeds across the country) has become the bottleneck. Do we really want to be the country that gets left behind by not advancing Internet infrastructure to its greatest achievement? That would be like saying, "I'll be fine with this old Pentium... I don't need anything newer or faster." There will always be advances in software that require more powerful hardware, and the same is true for the Internet.
And, let's be honest, if Google's Gigabit Internet came to your area and was cheaper than what you were paying for a 25-50Mbps connection, you would jump on it in a heart-beat. Assuming that you get good customer service from Google, then it would be foolish to pay more money for less performance.