Would you mind elaborating why you filmed in 4K?
Sure.
This:
do a bit of zooming in post production.
and...
and...
It's only a matter of time before everyone is on 4k and then we'll look back and wish all that 720/1080p stuff had twice the pixels.
Hard drives are cheap, memories are priceless.
I film everything in 4k these days, because it's cheap and I might as well. i like being able to punch in in post, and I like future-proofing it. If I need to go back and reuse any footage 5 years from now, 1080p will feel like 480p. The price point is cheap enough to make 4k a reality. Do I need to do it for YouTube content? Absolutely not, but it holds up better after grading and effects, and it gives me a lot of latitude for zooming in a little. That's especially worth it for GoPros, where it's already so tough to see something off in the distance.
Also, even if you're only publishing to 1080p, you'll still get a crisper video by filming and editing in 4k then exporting it down to 1080p. Each pixel is packed with that much more info, and you'll get a 'better' 1080p video. I don't know how to explain it better.
Is it worth it? I dunno. It's cheap, and it doesn't cost me any extra money to film in 4k. It takes one heck of a computer to edit it though. For most people it won't be worth it. For me, looking back at videos, I can definitely see a big difference between my 4k ones and my 1080p ones. Once you have a 2k, 3k, 4k, or 5k screen, it makes a huge difference.
I've still got a lot to learn, but this is my effort to make the best videos I know how, and when I look back at my time there I don't want to be saying "I wish I had just turned 4k on, it would have looked so much sharper."