I checked about post boost vehicles on the Minuteman I & II and couldn't find anything. Perhaps they didn't have one, but it seems to me that you just couldn't get the kind of precision you need for long range accuracy using solid propellants. Perhaps that's why they were armed with 1 MT warheads. The amount of hypergolic propellants in a PBV is very small compared to a Titan II. It's less than some satellites, so the chances of a catastrophic accident are much smaller.

When I read those reports about the recent Russian missile tests, they mentioned the possibility of using scramjet technology. I agree - that just doesn't make any sense. Most likely, the reporter simply got it wrong.

The only example of MARV technology that I know to enter service was the terminal guidance system on the Pershing II. That missile used a radar guidance system to activate small vanes to guide the warhead to the target. They had several failures during test flights before getting the bugs out of the system, but in the end, it reportedly worked very well. The goal of the Pershing II was increased accuracy rather than avoiding ABMs.

As for avoiding the ABMs currently in development, I don't see how the technology used on the Pershing II would help avoid interception. The mid course interceptor goes in for the kill while the missile is well above the atmosphere. If the missile carried an oversized PBV with a lot of propellant, you could possibly outmaneuver the interceptor by appearing to aim for one target, then changing course significantly after the interceptor is on its way. The interceptor can only change course by a given amount, so if you have enough propellant, you might be able to make it miss.