The fact that it is likely a K or A high flush is why i would reraise. If you think you're going to have a tough time folding the river to a bet such as the one given, then this is a cheaper way to see where you at in the hand while possibly forcing a fold.

Just a screwy idea i guess. Once again please criticize me if this makes no sense whatsoever, but i am also curious to know if my logic behind the play is OK.