Perhaps we could think of vanity as an enormous beast with a voracious appetite, constantly needing to be stroked and fed.

One whose character's "beginning and end" is vanity would seem to need more feeding, rather than less, since vanity is practically all that exists in there. ;o)

BTW, it has been my experience that the vainest, snootiest people are usually the most insecure -- e.g. they would be completely mortified if anyone they know saw then coming out of a Walmart! This is why Sir W. feels that "he would sooner quit Kellynch Hall at once, than remain in it on such disgraceful terms" (ch. 2).