The 30m CEP comes about because of the radar and guidence, all of which eat into warhead, which is fine if you have a penetrating nuke but no good if you have a blast/frag warhead. Id think that a salvo of 3-7 missiles with conventional warheads should be able to give a reasonable chance of hitting an airbase parking area, but the airbase should be packed with things like AWACS, Rivet Joints, JSTARS and tankers rather than fighter-bombers.
The Russians did use cluster warheads in the last few years, but they really need to be developed and deployed in the 60s to make TBMs a viable weapon. A cluster bomb warhead will drastically reduce the amount of TBMs needed to cover a soft target.
Nuke alerts is one of the things that would be very different if every Soviet client started throwing TBMs around from the 60s. Either NORAD and its Soviet counterpart would tune out certain parts of the world during crises or would become much better at detecting and tracking ballistic missile launches in order not to panic at every heat plume.