Razzo, on the upper point it does stand the shock up making it stiffer, but it also transfers weight quicker side to side giving a harder turn-in.
On point 1 you are spot on. When we first got the 415 the D blocks made the car too stiff for roll with the wide hinge-pin. As the rear got narrower the car came alive then we started running the old 414 parts until Tamiya released the A-bridge.
Anyone ever looked at the original Tech car. The hinge pins are prolly about 2mm each inboard of the current A position. Where our diff towers are is about where the hinge pins are on the MY-02.
Carl you have to be careful on how much wheel spacing you are using also as it alters the scrub radius on the steering knuckle. I look at it this way if the car is loose add spacing @ the hub to widen track width. Think of the old Pontiac commercial "wider is better". The other side is if you have alot of spacing and the car is glued then start narrowing up the track width. You should find the laptimes dropping and the car feels freer through the middle of the turn.
Along these lines this is why the old suspension works better with Foam. The new arms allow the car to roll and really create traction due to the narrow pin location.
You also add too much hub spacing to clear the steering arm causing the scrub radius to go to hell also.