Whoops!
Everything has now changed. I have cancelled both of the other reservations, and will be in Amsterdam City Centre, because my $142 bid on Priceline was accepted and I got the Hilton Amsterdam City Centre.... which, of course, isn't exactly in the centre--it's a 15-minute walk--but I am happy, especially considering the Hilton web site is selling the cheapest room for 375 Euros per night--and bookings.nl is showing availability for only 3 of 233 hotels in the city those nights!
Thanks so much for all your help, guys.