I emailed IC Duesseldorf re upgrades and was informed:
"For an Royal Ambassador we have following opportunities:
You book: Superior Room - and get an upgrade to Executive Room
You book: Deluxe Room - and get an upgrade to Executive Suite
You book: Club Room - and get an upgrade to Executive Suite
The highest category you will be upgraded to is Executive Suite. We do not offer upgrades to the club level."
Seemms slightly different to Plancktos was told - from my information there should have been no extra charge for the suite.