Can I restore pre-Mavericks power key behavior?
Since Mac OS 10.9.2 you can go back to something close to the pre-Mavericks behavior easily.

Type in terminal:
defaults write com.apple.loginwindow PowerButtonSleepsSystem -bool no

It's not exactly the same, since you still need to press the button for 1 sec. But if you press the button accidentally, the shut down dialog is not going to appear.

Note: if you want to go back to the Mavericks behavior, juste change no to yes.