Looking to stay in Hyatt chicago magnificent mile on thursday night (only night while I will be there that its not available). would it help if I purchased a suite upgrade from someone? If so, I would like to purchase one. TIA
I'm not sure that I properly understand your question, but if you are asking whether buying a DSU will help you get a room if no reward nights are available, the answer to the best of my knowledge is that it will not.
Also, for future reference, suite upgrades are usually given for free to be used for a qualifying stay (it's a win-win).