Well, do you or don't you like champions? That's really what it comes down to, and if you play with champions, you absolutely have to level them because they add to the multipliers in some cases, like the showdown event.
I turn them on and off, depending on the game, so they are not all good, and they are not all bad. It's just a modifier that you might feel like once in awhile. That being said, Ancient Shadows is the only one I really turn off, although I should consider turning off Spire so I can do this showdown event a little bit cleaner.