Mr. free101girl and I will be using Stay Certificates for the first time, at Grand Hyatt Kauai, Park Hyatt Tokyo and Park Hyatt Sydney. The certs will net us a significant savings vs. paying regular rates.

I know the certs are good only for a standard room. Neither of us is Diamond, so it's unlikely we'll get a free upgrade.

Has anyone here had any success with *paying* for an upgrade at check-in when using a stay cert? I have been able to buy upgrades at some Starwood properties when redeeming standard room awards, and it was often a bargain. Is it worth even trying this at Hyatt hotels?

Thanks for any insights.