I just wanted to note that most of my stays are LNF as well, and I have experienced the same thing as OP at many of them.

"wow, you got a nice rate *rolls eyes*"
"Yeah, I try. Do you happen to have any upgrades available?"
"Nope sorry we're full".

All the while the Marriott site will concurrently list purchasable suites...

Still well worth my time, since super low LNF rate rooms are worth far more to me than regularly priced upgrade rooms.