I think I could write the book on how to get a free hotel upgrade. Well, only when travelling on one's birthday, but I've done it more than once. Have done it twice in Hawaii and got bumped from parking lot view to ocean front view. I think the secret is to make it clear you don't expect it.... If they have room, I'm giving them an opportunity to play hero ;-)
My upcoming reservation in NYC next week was a truly rock bottom price through Priceline, but I still emailed them, told them I was celebrating my 50th birthday, and asked very nicely if they could upgrade me. The magic worked again. I got a nice email and an upgrade from the cheapest room in the hotel to a "club floor" room, which includes a lounge on the 44th floor with tvs, free coffee, breakfast, free appys, and more. And my room itself will be on the top floors (44-50) with all sorts of other stuff thrown in.