Spalting does soften some of the wood, after all it is a process of fungus decaying the wood to a point it becomes fungus food! But not all at once, the white areas are the ones that are usually softer, especially in advanced stages where it can degrade the wood to the point of uselessness, no structural strength left at all. In the early stages though you can have nice patterns and colouration (the black lines are zonal borders between different fungi) and yet the timber is still relatively sound, this is the best wood for turning with. What you get out of the woodpile or anywhere else apart from perhaps purchased blanks, is very much potluck.
Catching an edge? Do you mean getting a dig in with the tool? For logs turned between centres set the rest as close as possible at a point where the rotating wood just misses it and use a roughing gouge to turn it cylindrical. For a log mounted for a bowl Bring the tailstock up to support the base and set the rest the same and use a bowl gouge, taking off a little at a time across the piece until it becomes balanced, a gouge with a swept back style of grind is easier to use for this than a square grind.