The various ideas listed above fall down due to the fact that they try to find a compromise between the slash and burn of the ECB and the loyalties of existing supporters, however the ECB are not interested in compromise or existing supporters, Michael Vaughan's magic number is going to be even harder to attain due to the fact that some existing T20 watchers won't bother with the new competition and as we know it is a complete red herring to judge the validity of cricket attendance through comparison to football . If that criteria is used them out goes rugby union, league, horse racing, athletics and any sport that fails to attract 40,000 plus to every domestic fixture, indeed if Vaughan thinks a division two attendance level is inadequate then presumably he thinks football itself from that division down is not justifiable.
Incidentally, I read somewhere that 75% of the general public make up three quarters of the population.