you know,if you have a bad catalitic converter you should change it,changing your plugs and wires and opti spark will be useless if your cat it plugged.your just going to keep your engine under a constant unhealthy load,causing it to possibly over heat,foul plugs again,blow manifold gaskets,turn into a piece of crap.
you should park the car and fix it the right way,start with the known problems and go from there it makes no sense to change plugs when you know you have a bad cat.
having owned one of these i know repairs are pricey,but every time i did a repair on my formula it ran so much better.oh and it took me 3 hours to change my plugs. til one day i got wise and took the passenger side front wheel off and used a hole saw and cut a hole about as big around as a coke can in the wheel well just to make getting to that first plug a little easier and thats the only hard one on the whole car,i use to spray my LT1 so i had to stay on top of my plugs