Yes, yes and yes. I had a similar conversation with a REN Tampa Manager.
Extra towels, pillows, bed type, floors, room refrigerator, exercise equipment, etc will definitely override your chances of being upgraded since they will select and stock your pre-selected normal room accordingly.
I was told to leave it blank and when they see your PLT reservation, they'll "automatically" give you a King on the CL, if possible.
Don't know if it works accordingly everywhere. Love to hear other tricks and hints into getting "special rooms".
BTW, I think aiming for a Suite is way too high. But most hotels have special rooms called "Executive Rooms" or "Corner Kings" that are larger and usually contain a refrigerator. I think the trick is to find out what they are called at each property and request them by name.