I think it's always an advantage to have backward compatibility, for example, I am thinking of getting a Wii U mainly to play Zelda games, and it'd be annoying if I had to buy both consoles just to play a few games (added up, it's still only 3 xD). I do miss some of my Xbox original games that I had but now I'll have to buy another console just to play these older games.
I'd vote, but there isn't an option between "Ick, I never use backwards compatability!" and "I'd maybe get a console lacking it, but I really, really want it!". I would prefer my consoles to come with backwards compatibility, always. It's just nice to be able to play older games on them if I feel like it. But the console not having it isn't something that would keep me from buying. Of course I want it, but I don't need it, and I look at way more then that to decide whether I'm getting the system or not.
Very important to be honest. Not many people like their video games...if they support only the latest versions.
Sometimes people like the good old stuff.