Thats the thing. Nitrous works on any engine. As long as the engine isn't too weak to take it. So yes, it will work just fine on an spi. From what I usnderstand the spi is a very stout engine and can take the abuse. Put a 50 HP shot on it and have fun. As you said, do wet shot, much better set-up IMO.
Speed is only a matter of money; how fast do you want to go?