I love photopass. In March 2010 we went, stayed off-site, and I ended up ordering the CD after and it was $149. When my son and I went in November 2011 and stayed on-site, Disney sent a photopass card to use. I went ahead and pre-paid ($99). We didn't have as many pictures in November since it was a shorter trip with just us 2, and I don't think I would have paid full price for it, but would have at the reduced price.
I would think if you are going with kids, seeing character, going for more than 4 days... it would be worth it.