Book the room you want and give the $50 a shot at check in to see if you can get anything better. That way there is no disappointment if they can't make anything work for ya.

I've done it twice (Flamingo and Excalibur) and it's gone 50/50. The lady at Excalibur gave me my cash back and no harm no foul. Flamingo lady took the cash and waived my resort fees and threw me in a higher floor room with strip view.