A few observations on this thread.
Excellent analysis by FlyingDutch on how little difference going round CAS makes. In some cases like Andrewsfield, going South initially is the only option since you are so close to the edge of the Stansted CTR.
Beagle
Benson may have been dealing with intense gliding operations. Terseness on the radio is a fact of life; you and I both know we should not let it affect us.
Agree with overflying ATZs, 500 feet above might be safer. I often do it particularly when the frequency is busy, e.g. Cranfield. As was mentioned in another post, when the frequencies are busy it is normally good VMC.
MATZs are an anomaly not being CAS. However activity can increase rapidly at military aerodromes at time of tension, or for exercises. In the Lakenheath triangle near where I operate the recent Iraq situation meant that there was a significant increase in the numbers of heavy aircraft operating out of these 3 fields. Access to the CMATZ was not refused, but Lakenheath Radar had a better picture of traffic nearby.
IMHO to get the best chance of access to CAS it is necessary to sound competent on the radio. How many pilots ask for crossing clearance on their initial call? If you don't and get asked to standby, then get refused more time is wasted. Asking after providing your life story also makes the controllers disinclined to help. Asking to cross VFR in poor vis is not likely to be approved, if entry/exit lanes exist this might be OK, if you sound in control. Asking to cross a corner of the zone is pointless, as FlyingDutch says the saving in time will be insignificant. I read somewhere (possibly here) that a good idea is to plan avoiding CAS. If you get it then Plan B, take the shortcut and the saving.