I managed to get regular upgrades at Marriott, albeit this may have been due to emailing the hotel directly a week before my visit to request the upgrade. I don't think I ever failed to get an upgrade to the next category room. The emailing practice is one that have I continued since having moved most of my stays to Hilton (haven't stayed in a Marriott since November after the status match) albeit without much success being told that upgrades are based on availability on check-in rather than advance.

Nonetheless, at the original poster to this thread... I wanted to thank everybody for their time and help across the range of opinions each of which were valuable.

Simon.