My knowledge of the strategic arms agreements is pretty hazy, but I thought I remembered the ABM agreements to concern mostly static systems. The agreement, if I'm remembering right, allowed both the US and USSR to deploy a single system around a fixed geographic area - the Russians chose Moscow, and not too many years ago, it was still in 'operation,' although the operability of the interceptor vehicles was a major open question. The US retired it's system in the late 70's.
The ASAT system was tested in the very late 70's (in technical violation of the 'no development' agreements in some of the treaties), but was not pursued much past the development phase (although it was successfully tested against an operational satellite).
I would expect the big problem with wrecking a satellite is that you've got an uncontrolled thing up there when you're done. It's better than simply smashing it, 'cause a large single object is easier to track and plan around, but since it's uncontrollable, it'll be a lurking threat.
This kind of speculation is fun, although I'm stuck approaching it from the engineers point of view (which is basically throwing rocks at any and all ideas... heh).