There is also the psychological effect on the British and their allies - there is a big difference between a fortres which si seen to capitulate almost without fighting, and one which is finally taken after siege.
The effect on morale should be interesting, as historically the fall of Singapore came as a total shock yet was never truly explained to people here and in Britain. Even to this day new revelations (or at least analyses) about the failings of the AIF at Singapore are greeted with anger in this country, particularly if it comes from 'poms'. Max Hastings got a bit a of a bollicking recently for criticising the 8th Division in his new book about the Pacific War.
If Singapore holds out Bataan-like, but only holds up the Japanese rollover of Burma, the NEI and New Guinea by a month or so, then Australia will still be freaking out throughout 1942.
I wonder if this siege leads to more senior battle hardened officers escaping from Singapore ala Gordon Bennett.