Surely this would depend upon a number of things. The prestige of the particular beauty contest for a start. Those who reach the top level of these contests have to have far more than just physical beauty. They're expected to be intelligent, articulate, confident, and informed on world events. If they haven't got these non-physical qualities their chances of getting to such high-level contest is virtually nil.
However, if it's just a local and limited to a specific geographical area, it might well be that the majority of contestants in such contests achieve no more success, on average, than those who don't bother to enter.