You've always been able to increase a rejected bid, but you also must change the star level and/or location (zone).

To make sure nothing has changed, I just put in a $20 bid for a 4 star room in NYC for tomorrow night. Not only was the amount surely to be rejected, I know that NYC is sold out for tomorrow night.

So my bid was just rejected, and accompanied by the same language as has always accompanied a rejected bid:

TRY AGAIN RIGHT NOW TO GET A HOTEL ROOM IN NEW YORK, NY! If you can change one or more of the numbered items below, we'd be happy to resubmit your request right now. There's no cost to try your request again, and you'll have an answer in just one hour by e-mail.

Change at least one of the numbered items below, then click "Next".