Troy, I'm with you. Urine and ammonia are too closely related for either to do more than enhance the scent of the other. In fact, I don't believe there is anything that can truly mask the scent of cat spray well enough to hide it from the ultra-sensitive nose of a cat. You can put more unpleasant scents on top to dissuade them, or try a cleaner that uses a biological agent to dilute the scent to an acceptable level. What I've learned is if you can still see the urine stain under a black light (it will glow), then there's more than enough of the urine left for the cat to smell.

With all the cats I've fostered, I was lucky to never have a cat that spaying/neutering didn't stop their spraying, but I understand how extremely lucky I have been. Spaying/neutering helps in the majority of cases, but it depends on the age of the pet when it is altered and how active they were (sexually) before they were altered. Sometimes it doesn't stop the spraying.

I've heard of people who are allergic to cat that rinse their cats with club soda or quinine water or something like that (I don't remember which it was... maybe a combo of both??) but never knew anyone who actually tried it. Because of the dander from grooming, long haired cats are suppose to be much worse for people who have allergies (which is another reason why the hairless cats became popular in this area for a while - thanks to Austin Powers for the interest), but then again, everyone I know who is allergic thinks, "my allergy, my problem," so they treat themselves and don't put their pets through anything extra.