Have you had problems with it spitting back up through the carb because of something else wrong? These kits seem to be a big deal now, and I agree it would be a good safeguard against blowing out the power valve, but the power valves just don't "blow out" for no reason. There are many of these carbs running around without these protectors on them, and they are running fine.

When the power valve is leaking, the exhaust will smell rich, but the idle will usually be steady. I would look down the carb throat with a flashlight while the engine is idling, and see if you spot any liquid fuel dripping down into the engine. If you do, I suspect your float levels are too high in the bowls.