It really depends on the character to me. Some characters just aren't the same with out their suits, like Spiderman, Batman and Superman, where as others like Vanisher, Shatterstar and other lesser named characters should get their costume changes as it brings them into a modern age and makes them more iconic.
I live by the beach and go swimming every summer. One year I saw Jaws and learned there we dogfish swimming in the water. Needless to say, I stopped going in the water. Combined with the nuclear plant down the coast, you never know what scary radioactive sharks are in the water.
For X-Men I would suggest starting in the 490's, just when they move to San Francisco. And if you are a really new reader I would start with the awesome X-Men First Class series for a light hearted look at the original five.
Otherwise awesome list, I could have used this when I started reading.