You will not find a bigger fan of RB then me (well, maybe, but you'd have to search). But in my opinion, if you really want to learn guitar, get Rocksmith. I bought it for my son for xmas along with a $150 Fender Strat start up kit with amp. It was the best investment I've ever made for one of my kids, and I found myself playing it.
My son rips now. He played the game over and over again, not realizing that he was actually doing scales (it has these really cool game modes) or cord drills. He can play songs from the game without even having the game on now and is an amazing guitarist. (I still kick his butt at RB though!)
I'm ok, I don't put enough time in, but I can play some cords and don't do too bad at the game. It is super fun!!
I will never give up my RB game though. It's time to go back to playing now, cya.