It won't hurt the Apple TV to leave a song paused rather than putting it into standby, but since the screensaver, etc., will still run it'll eat more power and stay nice and hot (which I suppose might shorten it's lifespan a bit).
You don't, however, need to turn your TV back on and navigate through the menus to put the ATV into standby. Try this once or twice with the TV on so you can see how it works and I'm sure you'll be able to do it without looking at the menus:
1. While your music is playing (or from anywhere else, for that matter), hold down the Menu button on the ATV remote for about 3 - 5 seconds. That should bring up the main menu directly, rather than having to press "Menu" repeatedly to get back out step-by-step.
2. Once the main menu is displayed you don't have to navigate to the Standby option- just hold down the Play/Pause button on the remote for 5-10 seconds. You should see the screen go blank and the music stop as the ATV goes into Standby mode.
As you can see, that's fairly easy to do blind. I usually press Menu once to make sure it dismisses the screen saver if it's on, then hold Menu down for 5-10 seconds to make sure the menu is up, then just hold down Play/Pause until I hear whatever I was listening to stop playing.
Hope that helps. 🙂