Speaking of "smoothness" of difficulty, isn't one level above being twice a difficult a bit too steep? This could easily lead to circumstances where playing on your own level is too easy, but one level above is too hard. Sure, fiddling with the difficulty level could help ease this, but I wouldn't want to change from normal to easy difficulty every-time I wanted to be a little more adventurous but still live. How about something more gradual like 1.5x as difficult and continue on from there?