IME as a PLT (got nothing as GOLD), upgrades are a combination of 2 factors, regardless of how full the property is.

#1 - The property's attitude and willingness to PRE block you into an upgrade. Not by the front desk at check-in. Don't know why but IME properties Denver and West just seem to bend over back-wards and make it happen no how long your stay. I site Boulder, San Jose, Mesa, San Antonio Riverwalk, Sea-Tac FS and SD Marina who gladly do week long stays without the usually begging for it.

#2 - Your willingness to beg either at reservation comment (gone), virtual concierge, PLT line or at the front desk. Some times it works, sometimes not, mostly CL level is about it. Pre 2010, RI's were very, very willing to give 2BR's away. Now it seems to be a major chore for them to do so, I suspect an unpublicized chain-wide change in direction effective 1/1/10.

If a property has a hard line attitude against an upgrade since they want to charge extra for the room (Suite, Jr Suite, extra BR, corner room, CL room, view, etc), the Front Desk will be trained to deny it and they will creatively and politely lie about the reason why since you have no real hard way to refute it. Even at 10pm for a one night stay.

Just my experience being PLT since 2006. A predominately a solo business traveler, it really doesn't matter if the normal rooms are quite (as upgrades tend to be!) but their are other times I travel with the family and it would be nice to have space for worry free "relations" with one's spouse!

Again, purely my experience and conjecture.