First of all I think the Millers sound like an awesome deal, and whenever I do have the money to upgrade in the future, I'm 95% sure it'll be a set of either 1.6 or 1.7 ratio Millers (the other 5% is for if they are no longer available at the great price they are offered at now).
While overall rocker arm weight is not the best indicator of actual rocker inertia, as you guys are pointing out, the fact is that every part of the rocker that rotates contributes to it's moment of inertia. The parts that are further out from the rotational centerline, like the roller tip and the pushrod cup area, contribute the most... but all the rotating material contributes to the overall inertia.
Since it would be pretty difficult to compare the actual rotational inertia of all the different rockers, the next best thing would be to just compare their actual mass of moving parts (everything but the clips and trunion), and take a good look at where the mass appears to lie on the rocker body. On the Millers, they have a lot of material above the centerline of the roller tip, on the upper portion of the rocker body, which is the farthest out portion of the body from the rotational centerline, so that's why I brought the question up.
However, I'm still relatively new at this, and don't know how significant the rocker inertia is compared to the valve, spring, retainer, pushrod, and lifter. It would be nice to know how all those masses compare on a typical SBF. But if you guys say the difference is insignificant, then I'll take your word for it.