It takes like 5 seconds. You download the client, and you copy a folder to allow you to bypass the login screen. You do not need the crack for sandbox in order to watch replays. Plus there are websites like gamereplays.org where people rate the games, so technically you could find something more entertaining to watch with the benefits of playing it from your own computer (you chose what part of the map to view, better graphics, etc).
You're still missing the benefit of good commentary. I think there is absolute value in watching replays on your own machine, especially when you're analyzing your own game, but there is a lot to be said for the some of the commentary you get from people streaming. I've learned a hell of a lot listening to the people streaming from TeamLiquid.net, super informative.