I just opened a 2013 Favorites Collection and some of mine have hair issues too.
Pony's hair is perfect. It's even doing that magical self-curling that some g4s have.
Lyrica's is just a tad dry, but that's nothing a shampoo and conditioning won't take care of. Chrysalis has coarser hair, but it suits her so I don't mind.
Lyra and Diamond Tiara had nasty tangled messes. Lyra's felt oily at first, but looks and feels much better after a wash and overnight conditioning, and Diamond Tiara is receiving the same now.
Cadance is bait so I don't really care, and Shining Armor's troll hair doesn't count.