well, I believe dragon said it all best in his first posting on the RPG...
1. A stand off spike is just that: a device that iniates the shaped charge's detonation before it hits the side of the tank wall. this allows the shock cone to actually build-up and intensify, getting more bang for the buck before it hits the armor wall.
2. Theres really nothing special about a RPG warhead: you can jink around with the explosive (faster vs slower detonation) or the shape of the hollow inside (the cone that shapes the blast itself) but you dont have anything exotic, like depleted uranium or tungsten penetrators, like a kinetic kill weapon. I guess you could use these materials to act as a tamp behind the explosion, but it would make it an awful heavy item to carry for a average soldier, and the whole idea behind the RPG is mobile fire power.
3. A one in a gadzillion shot sounds about right. I havent heard about any tankers that have lost sleep over this.