Sure, but, macOS will upgrade, demanding more. My iMac is struggling a lot more, and it's just an OS update. If I put snow leopard on it again, it will fly. But it has new features and improvements, and performance improvements on some parts that I use. I wish I had invested in a better card.
And yes, video playback will go up as well. Even if you think it's just youtube. As time goes by and youtube and your bandwidth improves, you might process higher quality video automatically. And Chrome used to be so snappy and small footprint, it's a lot bigger now and more demanding. Javascript on web sites and much more complex css / svg / etc drawing cycles from the gpu/cpu as well.
Things change. And it's one reason why we feel the urge to upgrade.
If you have just the on board chip intel, I would strongly recommend upgrading to the one with the 460.
But the only reason to go from 455 to 460 is the double memory, and better performance, on a chip we all wish was a different one.
One thing I've learned over time with Apple products is that if you can choose to get a better video card for a hundred bucks, just do it. It's an investment you can't reconsider later.
But maybe I am just used to doing more graphics intense things with the system, and might have a different approach. Plus, others will simply have a different opinion about it.
I for one have a system and keep it until it basically breaks or doesn't let me do what i need from it anymore. Bought this mac in early 2009. I am so ready to replace it.