Can’t I just use a vertical laptop stand and plug the cables in manually?

Of course you can. But the DockBook is much, much cooler.

Why would I want to waste the MacBook’s gorgeous internal display?

It’s not a waste. That’s a great example of the sunk cost fallacy. You’ll still use it when you’re on the go, and it will still be just as beautiful.You’ll be much more productive on a large monitor. Try it!