"You may as well not bother fixing them if you're going to keep more than one. Cats do not share the litter box. One comandeers it and won't let the other use it or neither will use it."

No, please, FIX her anyway. There are a lot of other health benefits. Ask your vet. (Sorry, I'm an ex-vet tech. This borders on religion for a lot of us who are/were in the animal health field.)

But he's right about the litterbox thing. More cats need more litterboxes. Litterbox territoriality is a definite source of stress.

As far as neutered/spayed cats spraying--yes, some of them do, but it's usually stress-related or a urinary tract problem. Unneutered males do it to mark territory and it stinks to high Heaven (I would seriously rather have a skunk in the house). "Fixed" cats are much less likely to spray but other issues can bring on "inappropriate elimination". (Works for dogs, too. Male dogs neutered young are much less likely to urine-mark, especially indoors.)