In addition to hhoope01's points, I am upgraded to a suite at a full service property more than 80% of the time over the last two years by being friendly, asking the agent how their day was going and after confirming the number of nights I'm staying, I ask, "Do you happen to have a suite available for the platinum upgrade?"

As noted, most of the time they do. Especially at business hotels on weekend stays for one or two nights, but knowing your property is a good idea. And if they don't, I don't make a fuss as it is not part of the program, and a CL floor room isn't the worst thing in the world, especially if the lounge is left open for sodas and water. ^