Cracks: I can't tell whether the whole thing would fall apart without the tape, but you might want to consider carefully applying strong but pliable tape to the inside to hold it together and then remove the outside tape to improve the looks. Perhaps the helmet's cracks are just part of its use, such as a player slamming on the dugout floor, and I'm not sure you'd want to completely obscure that element of the helmet's use history.

Decal: There appears to be so much old pin tar on it that I don't see where there was ever a logo, and to apply a new logo, you'd have to remove pine tar which again is taking away an element of the use of the helmet.