Well I need them at 10.5 and can tell you that if I forget to use them all HE$$ breaks loose. I can count on one hand the times I have forgot.
As springer said 10.5 and up you need them, period.
I have seen a lot of complaints on hard starting builds lately in the 9.8 and 10.0 range and am wondering if someone is making mistakes on the decking of the heads/cylinder's, or pistons, or gaskets or what. I know at dead nuts on 10.0 there is no need for them in the friends bike I have ridden and started.
They do need cleaned no two ways about it. That is a very small hole into the chamber and if you are carboning up it will show with weak or sticky function of the releases.
Chuck is right on, on this point. I have also messed one of the holes up and needed to use a helcoil. That was spinning it out with just a socket and my hand, the only way I put those or plugs in, ever. Still happened. Now when I break them or a plug loose I spin it out a few turns and then spin back in, then out, just to make sure it is spinning and I am not cutting the threads coming out. NEVER thought as careful as I am that it could happen, it did.
Follow the sage advice given by others here and spend that money on something else until you really need them.
On the stealth thing, yea right. Most people don't see them or even know what they are, and if the bike is running, what the he$$ is stealth^rolleyez^